The Science of Diet & Exercise [PDF]

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The Science of Diet & Exercise

From the Editors of Scientific American Cover Image: malerapaso/Getty Images Letters to the Editor Scientific American One New York Plaza Suite 4500 New York, NY 10004-1562 or [email protected] Copyright © 2018 Scientific American, a division of Nature America, Inc. Scientific American is a registered trademark of Nature America, Inc. All rights reserved. Published by Scientific American www.scientificamerican.com ISBN: 978-1-2501-2158-5

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THE SCIENCE OF DIET & EXERCISE

From the Editors of Scientific American

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Table of Contents Introduction The Science of Diet & Exercise by Karin Tucker

SECTION 1 Breaking Biology: New Truths in Diet & Exercise 1.1 The Exercise Paradox by Herman Pontzer 1.2 The Messy Truth about Weight Loss by Susan B. Roberts and Sai Krupa Das 1.3 The “True” Human Diet by Peter Ungar 1.4 Mind over Meal: Weight-Loss Surgery and the Gut-Brain Connection by Bret Stetka

SECTION 2 Behavioral Intervention 2.1 Don’t Diet! by Charlotte N. Markey 2.2 Behavior: The Additional Key to Weight-Loss by David H. Freedman

SECTION 3 Mental Floss: Your Brain on Exercise 3.1 Head Strong by Ferris Jabr 3.2 Take 2 Hikes and Call Me in the Morning by Nathaniel P. Morris

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The Science of Diet & Exercise “It is easier to change a man's religion than to change his diet.” ― Margaret Mead Each year, Americans spend more than $60 billion to achieve their weight loss goals.1 On Amazon alone, a search for “diet” yields about 202,000 products, 193,000 of which are books. Search for “exercise” and you’ll find a whopping 841,000 products, 194,000 of which are books. It’s enough to make your head spin. What should be clear is that the solution isn’t simple. For years, the weight loss party line was one of basic math: burn more calories than you consume. Now, new evidence from Susan B. Roberts and Sai Krupa Das shows that the kinds of foods you eat are as important as how much you eat. This article and the seven others in this collection discuss the most recent research that’s upending conventional wisdom on weight loss and suggest ways to put that science to work for you. For example, it also seems inescapably logical that physically active people burn more calories, but studies of hunter-gatherers refute this notion. Anthropologist Herman Pontzer explores how energy expenditure (caloric burn) stays virtually constant among humans, regardless of the level of physical activity, indicating that exercise alone won’t help reach weight loss goals. The remaining selections take a look at the efficacy of the popular Paleolithic Diet and how weight-loss surgery impacts gut-brain communication in unexpected ways. The mind’s role is further explored in “Don’t Diet,” where psychologist Charlotte N. Markey lays out guidelines for weight-loss that help to avoid common psychological pitfalls of dieting. Then in “Behavior: The Additional Key to Weight-Loss,” David H. Freeman shows how the complexities of obesity can be circumvented by focusing on behavior in the same manner as treating stuttering or alcoholism. This is followed by two selections that take a look at how exercise and outdoor activity are effective treatments for depression and support increased overall mental health. Sorting out the details of the metabolic process and how weight management works is far more complicated than anyone initially thought. Simple fixes and one-size-fits-all advice has never worked, and often leads to cycles of failure, self-blame and depression. Now that evidence is starting to refute common dogmas surrounding weight loss, it opens doors for new approaches, both physical and mental, some of which can be applied to how we think about diet and exercise today. - Karin Tucker Book Editor

1. U.S. News & World Report. “The Heavy Price of Losing Weight,” by Geoff Williams. Jan. 2, 2013.

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SECTION 1 Breaking Biology: New Truths in Diet & Exercise

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The Exercise Paradox by Herman Pontzer Still no giraffe. Four of us had been walking half the day, tracking a wounded giraffe that Mwasad, a Hadza man in his late 30s, shot the evening before. He hit it in the base of the neck from about 25 yards with a steel-tipped, wood arrow smeared with powerful, homemade poison. Hadza are traditional hunter-gatherers who live off of wild plants and animals in the dry savanna wilder ness of northern Tanzania. They know the landscape and its residents better than you know your local Trader Joe’s. Mwasad had let the giraffe run to give the poison time to work, hoping to find it dead in the morning. An animal that size would feed his family and his camp for a week- but only if he could locate it. Mwasad led our party—Dave Raichlen from the University of Arizona, a 12-year-old Hadza boy named Neje and me—out of camp just after daybreak. Dave and I were of little use in this endeavor. Mwasad had invited us along as a friendly gesture and for the extra help to carry the butchered animal back to camp should our search effort succeed. As anthropologists who study human ecology and evolution, we jumped at the opportunity to tag along—Hadza men’s tracking abilities are legendary. It certainly beat the prospect of a long day in camp spent fiddling with research equipment. We walked hard for an hour through a pathless, rolling sea of golden, waist-high grass, dotted with brush and thorny acacia trees, directly to the bloody patch where the giraffe was struck. That bit of navigation in itself was quite a trick, like someone leading you to the middle of a 1,000-acre wheat field to show you where he had once dropped a toothpick and then nonchalantly reaching down to pick it up. Hour on hour, tracking the wounded animal under a relentless sun ensued as we followed ever more tenuous signs. Still no giraffe. At least I had water. We sat in the shade of some bushes just after midday, taking a break while Mwasad pondered where the injured creature might head. I had a quart or so left—enough, I figured, to get through the heat of the afternoon. Mwasad, however, had not brought any water with him, as is typical of the Hadza. As we packed up to restart the search, I offered him a drink. Mwasad gave me a sideways look, smiled and proceeded to drink the entire bottle in one long pull. When he finished, he casually handed me the empty bottle. It was karma. Dave and I, along with anthropologist Brian Wood from Yale University, had spent the past month living with the Hadza, conducting the first direct measurements of daily energy expenditure in a hunter-gatherer population. We enlisted a couple of dozen Hadza women and men, Mwasad among them, to drink small, incredibly expensive bottles of water enriched in two rare isotopes, deuterium and oxygen 18. Analyzing the concentration of those isotopes in urine samples from each participant would allow us to calculate their body’s daily rate of carbon dioxide production and thus their daily energy expenditure. This approach, known as the doubly labeled water method, is the gold standard in public health for measuring the calories burned each day during normal daily life. It is straightforward, completely safe and accurate, but it requires that participants drink every last drop of the enriched water. We had taken pains to make clear that they must not spill, that they had to finish the dose completely. Mwasad seemed to have taken that message to heart. Mwasad’s sly joking aside, my colleagues and I have learned a lot about how the human body burns calories through our work with the Hadza. Together with findings from investigators who study other populations, our research has revealed some surprising insights into human metabolism. Our data indicate that, contrary to received wisdom, humans tend to burn the same number of calories regardless of how physically active they are. Yet we have evolved to burn considerably more calories than our primate cousins do. These results help to explain two

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puzzles that might seem disparate at first but are, in fact, related: first, why exercise generally fails to aid weight loss and, second, how some of humanity’s unique traits arose. The Calorie Economy Researchers who are interested in human evolution and ecology often focus on energy expenditure because energy is central to everything in biology. One can learn a lot about any species by measuring its metabolism: life is essentially a game of turning energy into kids, and every trait is tuned by natural selection to maximize the evolutionary return on each calorie spent. Ideally, the study population lives in the same environments in which the species originally evolved, where the same ecological pressures that shaped its biology are still at work. That is difficult to achieve with human subjects because most people are divorced from the daily work of acquiring food from a wild landscape. For nearly all the past two million years, humans and our ancestors have been living and evolving as hunter-gatherers. Farming only got going about 10,000 years ago; industrialized cities and modern technology are only a few generations old. Populations such as the Hadza, one of the last hunter-gatherer populations left in the world, are key to understanding how our bodies evolved and functioned before cows, cars and computers. Life for the Hadza is physically demanding. Each morning the women leave the grass huts of camp in small groups, some carrying infants on their back in a wrap, foraging for wild berries or other edibles. Wild tubers are a staple of the Hadza diet, and women can spend hours digging them out of the rocky ground with sticks. Men cover miles each day hunting with bows and arrows they make themselves. When game is scarce, they use simple hatchets to chop into tree limbs, often 40 feet up in the canopy, to harvest wild honey. Even the children contribute, hauling buckets of water back from the nearest watering hole, sometimes a mile or more from camp. In the late afternoon, folks wend their way back to camp, sitting on the ground and talking around small cooking fires, sharing the day’s returns and tending to the kids. Days roll along like this through dry and wet seasons, ad millennium. But forget any romantic notions of some lost Eden. Hunting and gathering is cerebral and risky, a high-stakes game in which the currency is calories and going bust means death. Men such as Mwasad spend hundreds of calories a day hunting and tracking, a gamble that they hope will pay off in game. Savvy is just as critical as stamina. Whereas other predators can rely on their speed and strength to obtain prey, humans have to outthink their quarry, considering their behavioral tendencies and scouring the landscape for signs of game. Still, Hadza men land big game like giraffes only about once a month. They would starve if Hadza women were not executing an equally sophisticated, complementary strategy, using their encyclopedic knowledge of local plant life to bring home a reliable bounty every day. This complex, cooperative foraging is what made humans so incredibly successful and is the core of what makes us unique. Researchers in public health and human evolution have long assumed that our hunter-gatherer ancestors burned more calories than people in cities and towns do today. Given how physically hard folks such as the Hadza work, it seems impossible to imagine otherwise. Many in public health go so far as to argue that this reduction in daily energy expenditure is behind the global obesity pandemic in the developed world, with all those unburned calories slowly accumulating as fat. One of our motivations for measuring Hadza metabolism was to determine the size of this energy shortfall and see just how deficient we Westerners were in our daily expenditure. Back home in the U.S. after a hot and dusty field season, I lovingly packed the vials of Hadza urine on dry ice and sent them away to the Baylor College of Medicine, home of one of the best doubly labeled water laboratories in the country, imagining the whopping calorie totals they would reveal. But a funny thing happened on the way to the isotope ratio mass spectrometer. When the analyses came back from Baylor, the Hadza looked like everyone else. Hadza men ate and burned about 2,600 calories a day, Hadza women about 1,900 calories a day—the same as adults in the U.S. or Europe. We looked at the data every way imaginable, accounting for effects of body size, fat percentage, age and sex. No difference. How was it possible? What were we missing? What else were we getting wrong about human biology and evolution? Lies My Fitbit Told Me It seems so obvious and inescapable that physically active people burn more calories that we accept this paradigm without much critical reflection or experimental evidence. But since the 1980s and 1990s, with the

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advent of the doubly labeled water method, the empirical data have often challenged the conventional wisdom in public health and nutrition. The Hadza result, strange as it seemed, was not some thunderbolt from the blue but more like the first cold drop of water down your neck from a rain that had been building, ignored, for years. The earliest doubly labeled water studies among traditional farmers in Guatemala, the Gambia and Bolivia showed their energy expenditures were broadly similar to those of city dwellers. In a study published in 2008, Amy Luke, a researcher in public health at Loyola University Chicago, took this work a step further, comparing energy expenditure and physical activity in rural Nigerian women with that in African-American women in Chicago. Like the Hadza study, hers found no differences in daily energy expenditure between populations, despite large differences in activity levels. Following up on that work, Lara Dugas, also at Loyola, along with Luke and others, analyzed data from 98 studies around the globe and showed that populations coddled by the modern conveniences of the developed world have similar energy expenditures to those in less developed countries, with more physically demanding lives. Humans are not the only species with a fixed rate of energy expenditure. On the heels of the Hadza study, I piloted a large collaborative effort to measure daily energy expenditure among primates, the group of mammals that includes monkeys, apes, lemurs and us. We found that captive primates living in labs and zoos expend the same number of calories each day as those in the wild, despite obvious differences in physical activity. In 2013 Australian researchers found similar energy expenditures in sheep and kangaroos kept penned or allowed to roam free. And in 2015 a Chinese team reported similar energy expenditures for giant pandas in zoos and in the wild. For a more granular look, comparing individuals instead of population averages, I recently joined Luke and her team, including Dugas, to examine activity and energy expenditure in a large, multiyear analysis known as the Modeling the Epidemiological Transition Study (METS). More than 300 participants wore accelerometers similar to a Fitbit or other fitness tracker 24 hours a day for an entire week while their daily energy expenditure was measured with doubly labeled water. We found that daily physical activity, tracked by the accelerometers, was only weakly related to metabolism. On average, couch potatoes tended to spend about 200 fewer calories each day than people who were moderately active: the kind of folks who get some exercise during the week and make a point to take the stairs. But more important, energy expenditure plateaued at higher activity levels: people with the most intensely active daily lives burned the same number of calories each day as those with moderately active lives. The same phenomenon keeping Hadza energy expenditure in line with that of other populations was evident among individuals in the study. How does the body adjust to higher activity levels to keep daily energy expenditure in check? How can the Hadza spend hundreds of calories a day on activity yet burn the same total number of calories a day as comparatively sedentary people in the U.S. and Europe? We are still not sure, but the cost of activity per se is not changing: we know, for example, that Hadza adults burn the same number of calories to walk a mile as Westerners do. It could be that people with high activity levels change their behavior in subtle ways that save energy, like sitting rather than standing or sleeping more soundly. But our analysis of the METS data suggests that although these behavioral changes might contribute, they are not sufficient to account for the constancy seen in daily energy expenditure. Another intriguing possibility is that the body makes room for the cost of additional activity by reducing the calories spent on the many unseen tasks that take up most of our daily energy budget: the housekeeping work that our cells and organs do to keep us alive. Saving energy on these processes could make room in our daily energy budget, allowing us to spend more on physical activity without increasing total calories spent per day. For example, exercise often reduces inflammatory activity that the immune system mounts as well as levels of reproductive hormones such as estrogen. In lab animals, increased daily exercise has no effect on daily energy expenditure but instead results in fewer ovulatory cycles and slower tissue repair. And extremes may lead some animals to eat their own nursing infants. Humans and other creatures seem to have several evolved strategies for keeping daily energy expenditure constrained. All of this evidence points toward obesity being a disease of gluttony rather than sloth. People gain weight when the calories they eat exceed the calories they expend. If daily energy expenditure has not changed over the course of human history, the primary culprit in the modern obesity pandemic must be the calories consumed. This should not be news. The old adage in public health is that “you can’t outrun a bad diet,” and experts know from personal

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experience and lots of data that just hitting the gym to lose weight is frustratingly ineffective. But the new science helps to explain why exercise is such a poor tool for weight loss. It is not that we are not trying hard enough. Our bodies have been plotting against us from the start. You still have to exercise. This article is not a note from your mom excusing you from gym class. Exercise has tons of well-documented benefits, from increased heart and immune system health to improved brain function and healthier aging. In fact, I suspect that metabolic adaptation to activity is one of the reasons exercise keeps us healthy, diverting energy away from activities, such as inflammation, that have negative consequences if they go on too long. For example, chronic inflammation has been linked to cardiovascular disease and autoimmune disorders. The foods we eat certainly affect our health, and exercise paired with dietary changes can help keep off unwanted pounds once a healthy weight has been reached, but evidence indicates that it is best to think of diet and exercise as different tools with different strengths. Exercise to stay healthy and vital; focus on diet to look after your weight. Energy Budgets and Evolution Even as the recent science in metabolic adaptation helps to clarify the relation between exercise and obesity, a constrained, adaptive metabolism leaves researchers with larger, existential questions. If daily energy expenditure is virtually immobile, how could humans evolve to be so radically different from our ape relatives? Nothing in life is free. Resources are limited, and investing more in one trait inevitably means investing less in another. It is no coincidence that rabbits reproduce prodigiously but die young; all that energy plowed into offspring means less for bodily maintenance and longevity. Tyrannosaurus rex can thank its big head of nasty teeth and powerful hind limbs for its puny arms and hands. Even dinosaurs couldn’t have it all. Humans flout this bedrock evolutionary principle of austerity. Our brains are so large that, as you sit reading this article, the oxygen from every fourth breath you take is needed just to feed your brain. Yet humans have bigger babies, reproduce more often, live longer and are more physically active than any of our ape relatives. Hadza camps are full of cheerfully chaotic children and hale, hearty men and women in their 60s and 70s. Our energetic extravagance presents an evolutionary puzzle. Humans are so genetically and biologically similar to other apes that researchers have long assumed that our metabolisms are similar, too. But if energy expenditures are as constrained as our Hadza study and others suggest, how could an inflexible, apelike metabolism process all the calories needed to support our costly human traits? In the wake of our broad, comparative primate energetics study, my colleagues and I began to wonder whether humans’ adaptive suite of energetically costly traits was fueled by a wholesale evolutionary change in metabolic physiology. We had found in that study that primates burn only half as many calories a day as other mammals do. The reduced metabolic rates of primates correspond with their slow rates of growth and reproduction. Perhaps, conversely, the faster reproduction and other expensive traits of humans were linked to the evolution of an increased metabolic rate. All that was needed to test this idea was getting a bunch of frenetic chimpanzees, wily bonobos, phlegmatic orangutans and skittish silverback gorillas to carefully drink doses of doubly labeled water without spilling and to provide a few urine samples. In a scientific tour de force, my colleagues Steve Ross and Mary Brown, both at Lincoln Park Zoo in Chicago, worked with caretakers and veterinarians from more than a dozen zoos across the U.S. to pull that off. It took a couple of years, but they accumulated enough data on great ape energy expenditure to provide a solid comparison with humans. Sure enough, humans burn more calories each day than any of our great ape relatives. Even after accounting for effects of body size, activity level and other factors, humans consume and expend about 400 more calories a day than chimpanzees and bonobos do; differences with gorillas and orangutans are larger still. Those extra calories represent the extra work our bodies do to support larger brains, produce more babies and maintain our bodies so we live longer. It is not simply that we eat more than other apes (although we do that, too); as we know all too well, piling extra calories into a body that is not equipped to use them only results in obesity. Our bodies, right down to the cellular level, have evolved to burn energy faster and get more done than our ape relatives. Human evolution was not entirely without trade-offs: our digestive tract is smaller and less costly than other apes, which need a large, energetically expensive gut to digest their fibrous, plant-based diets. But the critical changes that make us

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human were fueled by an evolutionary shift in our metabolic engine. Shared Fortunes At some point in the late afternoon, our path bent toward camp, Mwasad looking ahead instead of searching the ground. We were heading home sans giraffe. Here was the fundamental danger in the high-energy human strategy: coming home empty-handed was both more likely and more consequential. Many of the energy-rich foods we need to fuel our faster metabolisms are inherently difficult to obtain in the wild, increasing the energy cost of finding food and heightening the risk of starvation for the men and women out foraging and their kids back at camp. Happily for Mwasad, humans have evolved a few tricks to keep starvation at bay. We are the only species that has learned to cook, which increases the caloric value of many foods and makes them more efficient to digest. Our mastery of fire converts otherwise inedible root vegetables—from Trader Joe’s yams to wild Hadza tubers—into veritable starch bombs. We have also evolved to be fat. We know this all too well from the obesity crisis in the West, but even Hadza adults, lean by any human standard, carry twice as much fat as chimpanzees idling away in zoos. Problematic though it may be in our modern era, our propensity to store fat most likely coevolved with our faster metabolism as a critical energy buffer to survive lean times. As the sun sat heavy and orange just above the trees, we melted back into camp, Dave and I toward our tents, Mwasad and Neje to their families’ huts, each one of us glad to be home. Despite the lost giraffe, no one went hungry that evening. Instead, with little fanfare or conscious effort, the camp deployed our species’ most ingenious and powerful weapon against starvation: sharing. Sharing food is so fundamental to the human experience, the common thread of every barbecue, birthday, bar mitzvah, that we take it for granted, but it is a unique and essential part of our evolutionary inheritance. Other apes do not share. Beyond our nutritional requirements and fixation with fat, perhaps the most profound impact of our increased energy expenditure is this human imperative to work together. Evolving a faster metabolism bound our fortunes to one another, requiring that we cooperate or die. As I sat with Dave and Brian, recounting the day’s adventures over tinned sardines and potato chips, I realized I would not have had it any other way. No giraffe, no problem

Credit: Graphic by Jen Christiansen Sources: “Hunter-Gatherer Energetics and Human Obesity,” by Herman Pontzer et al., In Plos One, Vol. 7, No. 7, Article No. E40503; July 25, 2012; “Metabolic Acceleration and the Evolution of Human Brain Size and Life History,” by Herman Pontzer et al., In Nature, Vol. 533; May 19, 2016.

--Originally published: Scientific American 316(2); 26-31 (February 2017).

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The Messy Truth about Weight Loss by Susan B. Roberts and Sai Krupa Das The global obesity epidemic is one of the greatest health challenges facing humanity. Some 600 million, or 13 percent, of the world’s adults were obese in 2014—a figure that had more than doubled around the globe since 1980. At present, 37 percent of American adults are obese, and an additional 34 percent are overweight. If current trends continue, health experts predict that half of all Americans will be obese by 2030. If fad diets, reality television programs and willpower could make a dent in the problem, we would have seen a change by now. Obesity (characterized by excess body fat and measured as 120 percent or more of ideal weight) is much too complex to be solved with quick fixes, however. Figuring out why we eat what we eat, how the body controls weight and how best to get people to change unhealthy habits is not easy. Our laboratory has spent the past two decades trying to develop, with all the rigor that science allows, more effective methods for treating obesity and maintaining a healthy weight. Much of our work has challenged common dogmas and opened doors for new approaches. We have shown, for example, that exercise is not the most important thing to focus on when you want to lose weight—although it has numerous other health benefits, including maintaining a healthy weight. As many experts have suspected and as we and others have now proved, what you eat and how much you eat play a substantially greater role in determining whether you shed kilograms. But our research has gone much deeper, showing that different people lose weight more effectively with different foods. This realization allows us to create personalized weight-loss plans for individuals that work better than any one-size-fits-all advice. We believe this new understanding could improve the health of millions of people around the world. Obesity increases the risk of all the major noncommunicable diseases, including type 2 diabetes, heart disease, stroke and several types of cancers— enough to decrease a person’s potential life span by as much as 14 years. Research shows that excessive weight also interferes with our body’s ability to fight off infections, sleep deeply and age well, among other problems. It is long past time for us to understand how to combat this epidemic.

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Credit: Source CDC

Fuel-Efficient Losing weight can be reduced to a simple mathematical formula: burn more calories than you consume. For decades health experts figured that it did not matter too much how you created that deficit: as long as you got the right nutrients, you could safely lose weight with any combination of increased exercise and reduced consumption of food. But this assumption does not take into account the complexities of human physiology and psychology and so quickly falls apart when tested against real-world experience . As it happens, sorting out the details and putting weight management on a more scientific footing have taken much longer and have required a wider range of expertise than anyone had expected. Our first step, beginning in the 1990s, was to determine a base requirement: How much energy does it take to fuel the average human body? This straightforward question is not easy to answer. People get their energy from food, of course. But for individuals to use that energy, the food must be broken down or metabolized to become the equivalent of gasoline for a car. The oxygen we breathe helps to burn that fuel, and whatever is not used right away is stored in the liver as glycogen (a form of carbohydrate) or fat. When no more space is available in the liver, the excess is stored elsewhere in fat cells. In addition, metabolism creates carbon dioxide, which we exhale, as well as other waste products that are excreted as urine and feces. The process runs at different levels of efficiency in different individuals and under different circumstances in the same individual. For a long time the best way to measure people’s energy expenditure was to have them live for two weeks in a specialized lab, such as ours, where researchers could measure everything subjects eat and track their weight. Another way was to put volunteers in a sealed room (called a calorimeter) and measure the oxygen they breathe and the carbon dioxide they exhale. From these measurements we could assess the body’s basic energy requirements. Neither method is terribly convenient, and neither does a good job of replicating the conditions of everyday life. A much easier approach uses so-called doubly labeled water, which contains tiny amounts of deuterium (2H) and

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oxygen 18 (18O), both harmless, nonradioactive isotopes. For one to two weeks after a person drinks doubly labeled water, the body excretes the deuterium and some of the oxygen 18 in urine. (The rest of the oxygen 18 is exhaled as carbon dioxide.) Investigators take urine samples and compare how quickly these two isotopes disappear from the body during that time. With these data, they can calculate the number of calories an individual burns without interrupting his or her daily routine. The method was developed in the 1950s, but for decades doubly labeled water was too expensive to use in people. By the 1980s prices had dropped, and the technique had become more efficient, although there were times when our lab had to spend as much as $2,000 to perform a single measurement. As a result, it took more than 20 years to accumulate enough data to figure out how much energy the body needs to avoid weight gain or loss. These experiments—conducted by our group and others—helped us determine that humans do not need a lot of calories to stay healthy and active. And any excess consumption quickly results in weight gain. In this respect, we are much like other primates, including chimpanzees and orangutans. An adult male of healthy weight and typical height living in the U.S. today requires about 2,500 calories per day to maintain his weight, whereas the average nonobese adult female requires around 2,000 calories. (Men tend to use more calories because, on average, they have larger bodies and greater muscle mass.) In contrast, studies show that species as diverse as red deer (Cervus elapus, average weight 100 kilograms for the six-year-old females in one experiment) and gray seals (Halichoerus grypus, average weight 120 kilograms for three adult females) require two to three times more calories, kilogram per kilogram, than primates to maintain their size. It is tempting to assume that Americans have low calorie requirements because they lead sedentary lives, but researchers have documented similar calorie needs even in indigenous populations leading very active lives. Herman Pontzer of Hunter College and his colleagues measured the calorie requirements of the Hadza people in northern Tanzania, a group of hunter-gatherers, and found that the men needed 2,649 calories on average per day. The women, who—like the men—tend to be smaller than counterparts in other regions, needed just 1,877. Another study of the indigenous Yakut people of Siberia found requirements of 3,103 calories for men and 2,299 for women. And members of the Aymara living in the Andean altiplano were found to require 2,653 calories for men and 2,342 calories for women. Although our calorie requirements have not changed, government data show that, on average, Americans consume 500 more calories (the equivalent of a grilled chicken sandwich or two beef tacos at a fast-food restaurant ) each day than they did in the 1970s. An excess of as little as 50 to 100 calories a day—the equivalent of one or two small cookies—can lead to a gain of one to three kilograms a year. That easily becomes 10 to 30 kilograms after a decade. Is it any wonder, then, that so many of us have become overweight or obese? Complicated Calories The formula for maintaining a stable weight—consume no more calories than the body needs for warmth, basic functioning and physical activity—is just another way of saying that the first law of thermodynamics still holds for biological systems: the total amount of energy taken into a closed system (in this case, the body) must equal the total amount expended or stored. But there is nothing in that law that requires the body to use all sources of food with the same efficiency. Which brings us to the issue of whether all calories contribute equally to weight gain. Research in this area is evolving, and understanding why it has taken so long to get definitive answers requires a trip back in history to the late 1890s and the tiny community of Storrs, Conn. There a chemist by the name of Wilbur O. Atwater built the first research station in the U.S. designed to study the production and consumption of food. In fact, Atwater was the first to prove that the first law of thermodynamics holds for humans as well as animals. (Some scientists of his day thought people might be an exception to the rule.) The experimental design of metabolic labs has changed remarkably little since Atwater’s day. To determine how much energy the body can derive from the three major components of food—proteins, fats and carbohydrates—he asked a few male volunteers to live, one at a time, inside a calorimeter for several days. Meanwhile Atwater and his colleagues measured everything each human guinea pig ate, as well as what became of that food, from the

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carbon dioxide the volunteer exhaled to the amounts of nitrogen, carbon and other components in his urine and feces. Eventually the researchers determined that the body can extract about four calories of energy per gram from proteins and carbohydrates and nine calories per gram from fat. (These numbers are now known as Atwater factors.) Food does not come to us as pure protein, carbohydrate or fat, of course. Salmon consists of protein and fat. Apples contain carbohydrates and fiber. Milk contains fat, protein, carbohydrates and a lot of water. It turns out that a food’s physical properties and composition play a greater role in how completely the body can digest and absorb calories than investigators had anticipated. In 2012, for example, David Baer of the U.S. Department of Agriculture’s Beltsville Human Nutrition Research Center in Maryland proved that the body is unable to extract all the calories that are indicated on a nutritional label from some nuts, depending on how they are processed. Raw whole almonds, for example, are harder to digest than Atwater would have predicted, so we get about a third fewer calories from them, whereas we can metabolize all the calories found in almond butter. Whole grains, oats and high-fiber cereals are also digested less efficiently than we used to think. A recent study by our team looked at what happened when volunteers consumed a whole-grain diet that included 30 grams of dietary fiber versus more typical American fare that contained half as much fiber. We detected an increase in the number of calories lost to the feces, as well as a bump in metabolism. Together these changes amounted to a net benefit of nearly 100 calories a day—which can have a substantial effect on weight over a period of years. And so we and others have proved that not all calories are equal—at least for nuts and high-fiber cereals. As scientists learn more about how efficiently different foods are digested and how they affect the body’s metabolic rate, we will likely see some other examples of such disparities that are just large enough to influence how easy— or hard—individuals find managing their weight. Energy Expenditure So much for what we put in our mouth. What our body does with the food we eat brings us to the other side of the energy balance equation—energy expenditure. Researchers are discovering a surprising deal of variability here as well. One of the most common pieces of advice that people get when they are trying to lose weight is that they should exercise more. And physical activity certainly helps to keep your heart, brain, bones and other body parts in good working order. But detailed measurements conducted in our lab and others show that physical activity is responsible for only about one third of total energy expenditure (assuming a stable body weight). The body’s basal metabolism—that is, the energy it needs to maintain itself while at rest—makes up the other two thirds. Intriguingly, the areas of the body with the greatest energy requirement are the brain and certain internal organs, such as the heart and kidneys—not the skeletal muscle, although strength training can boost basal metabolism modestly. In addition, as anyone who has ever reached middle age understands all too well, metabolism changes over time. Older people need fewer calories to keep their body running than they did in their youth. Metabolic rate also differs among individuals. One study published in 1986 measured the metabolic rates of 130 people from 54 families. After accounting for differences in age, gender and body composition, investigators reported variability among families of around 500 calories a day. The inescapable conclusion: when it comes to metabolic rate—and your ability to lose or maintain your weight—parentage makes a difference. But let us suppose that you have started to lose some weight. Naturally, your metabolic rate and calorie requirements must fall as your body becomes smaller, meaning that weight loss will slow down. That is just a matter of physics: the first law of thermodynamics still applies. But the human body is also subject to the pressures of evolution, which would have favored those who could hold on to their energy stores by becoming even more fuel-efficient. And indeed, studies show that metabolic rate drops somewhat more than expected during active weight loss. Once a person’s weight has stabilized at a new, lower level, exercise can help in weight management by compensating for the reduced energy requirement of a smaller body.

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Hungry Brains Variations in Atwater factors and metabolic rates are not the end of the story. A growing body of research has demonstrated that our brain plays a central role, coordinating incoming signals from a wide range of physiological sensors in the body while alerting us to the presence of food. The brain then creates sensations of hunger and temptation to make sure that we eat. In other words, the role of hunger has long been to keep us alive. Thus, there is no point in fighting it directly. Instead one of the keys to successful weight management is to prevent hunger and temptation from happening in the first place. Single-meal feeding tests by several labs, including our own, show that meals higher in protein or fiber or those that do not cause a sudden spike in blood sugar (glucose) levels are generally more satisfying and better at suppressing hunger. (Carbohydrates are the most common source of glucose in the blood, but proteins can generate it as well.) A summary one of us (Roberts) published in 2000 indicated that calorie consumption in the hours following a breakfast with a so-called high glycemic index (think highly processed breakfast cereals) was 29 percent greater than after a morning meal with a low glycemic index (steel-cut oatmeal or scrambled eggs). In fact, our team recently obtained the first preliminary data showing that it is possible to reduce hunger during weight loss by choosing the right foods. Before assigning 133 volunteers to one of two groups, we asked them to answer a detailed questionnaire about how often, when and how intensely they were hungry. Then we randomly assigned subjects to either a weight-loss program that emphasized foods high in protein and fiber and low in glycemic index (fish, beans, apples, vegetables, grilled chicken and wheat berries, for example) or to a “waiting list,” which served as the control group. Remarkably, over the course of six months members of the experimental group reported hunger levels that decreased to below the values measured before the program began. We noticed a difference on the scales as well. By the end of the study, they had also lost an average of eight kilograms, whereas the control group had gained 0.9 kilogram. Just as interesting, the intervention group experienced fewer food cravings as well, which suggests that what their brains perceived as pleasurable had changed. We then scanned the brains of 15 volunteers as they viewed pictures of a wide range of foods. The results showed that the reward center of the brain became more active over time in the intervention group in response to pictures of grilled chicken, whole-wheat sandwiches and fiber cereal. Meanwhile that group’s brains became less responsive to images of french fries, fried chicken, chocolate candies and other fattening foods. The Energy Equation The laws of thermodynamics apply to biological organisms just as much as anything else in the universe. The number of calories that we absorb from food has to equal the number of calories our body either expends or stores. But the simplest methods for balancing this equation are not necessarily the most true to life. Individuals do not, for example, process all foods equally effectively. And different people require different amounts of energy just to keep their body humming. The graphic illustrates a few of the known complexities.

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Credit: Graphic by Brown Bird Design (food illustrations) and Amanda Montañez. Sources: U.S. Department of Agriculture Food Composition Databases (food data); “High-Protein Weight-Loss Diets: Are They Safe and Do They Work? A Review of the Experimental and Epidemiologic Data,” by Julie Eisenstein et al., In Nutrition Reviews, Vol. 60, No. 7; July 2002 (thermic effect data ); Human Energy Requirements: Report of a Joint FAO/WHO/UNU Expert Consultation. World Health Organization, Food and Agriculture Organization of the United Nations and United Nations University. FAO 2001 (basal metabolism data ); “High Glycemic Index Foods, Overeating, and Obesity,” by David S. Ludwig et al., In Pediatrics, Vol. 103, No. 3; March 1999 (glycemic index data).

Personalized Diets Differences in the hunger-reducing properties of foods, the efficiency with which they are absorbed and the real, though limited, ability of our metabolism to adapt to changes in energy intake make weight management a complex system. We keep finding special circumstances that affect various people differently. For example, it has been well established that the majority of individuals who are obese secrete proportionately higher levels of insulin, the hormone that helps the body to metabolize glucose. This so-called insulin resistance leads to a host of other metabolic problems, such as increased risk of heart attack or developing type 2 diabetes. When we placed such people on a six-month weight-loss program featuring more protein and fiber, fewer carbohydrates and a low glycemic index, we found that they lost more weight than they could on a high-carbohydrate diet with a high glycemic index. People with low insulin levels, in contrast, did equally well on diets that were higher or lower in the ratio of proteins and carbohydrates, as well as in glycemic index. Today we regularly help our study volunteers lose weight and keep it off. Despite the fact that our 133-volunteer investigation, described earlier, was six months long and required participants to attend weekly meetings and reply to e-mails during most of that time, only 11 percent dropped out. Some even cried at the re search team’s final visit because they did not want to say goodbye. Not only had they lost weight, but they had been so much more successful than they expected that they felt transformed psychologically as well as physically. In the words of one participant, “the science worked.” --Originally published: Scientific American 316(6); 36-41 (June 2017).

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The “True” Human Diet by Peter Ungar People have been debating the natural human diet for thousands of years, often framed as a question of the morality of eating other animals. The lion has no choice, but we do. Take the ancient Greek philosopher Pythagoras, for example: “Oh, how wrong it is for flesh to be made from flesh!” The argument hasn’t changed much for ethical vegetarians in 2,500 years, but we also have Sarah Palin, who wrote in Going Rogue: An American Life, “If God had not intended for us to eat animals, how come He made them out of meat?” Have a look at Genesis 9:3. While humans don’t have the teeth or claws of a mammal evolved to kill and eat other animals, that doesn’t mean we aren’t “supposed” to eat meat, though. Our early Homo ancestors invented weapons and cutting tools in lieu of sharp carnivore-like teeth. There’s no explanation other than meat eating for the fossil animal bones riddled with stone tool cut marks at fossil sites. It also explains our simple guts, which look little like those evolved to process large quantities of fibrous plant foods. But gluten isn’t unnatural either. Despite the pervasive call to cut carbs, there’s plenty of evidence that cereal grains were staples, at least for some, long before domestication. People at Ohalo II on the shore of the Sea of Galilee ate wheat and barley during the peak of the last ice age, more than 10,000 years before these grains were domesticated. Paleobotanists have even found starch granules trapped in the tartar on 40,000-year-old Neandertal teeth with the distinctive shapes of barley and other grains, and the telltale damage that comes from cooking. There’s nothing new about cereal consumption. This leads us to the Paleolithic Diet. As a paleoanthropologist I’m often asked for my thoughts about it. I’m not really a fan—I like pizza and French fries and ice cream too much. Nevertheless, diet gurus have built a strong case for discordance between what we eat today and what our ancestors evolved to eat. The idea is that our diets have changed too quickly for our genes to keep up; and the result is said to be “metabolic syndrome,” a cluster of conditions including elevated blood pressure, high blood-sugar level, obesity, and abnormal cholesterol levels. It’s a compelling argument. Think about what might happen if you put diesel in an automobile built for regular gasoline. The wrong fuel can wreak havoc on the system, whether you’re filling a car or stuffing your face. It makes sense, and it’s no surprise that Paleolithic diets remain hugely popular. There are many variants on the general theme, but foods rich in protein and omega-3 fatty acids show up again and again. Grass-fed cow meat and fish are good, and carbohydrates should come from nonstarchy fresh fruits and vegetables. On the other hand, cereal grains, legumes, dairy, potatoes, and highly refined and processed foods are out. The idea is to eat like our Stone Age ancestors—you know, spinach salads with avocado, walnuts, diced turkey, and the like. I am not a dietician, and cannot speak with authority about the nutritional costs and benefits of Paleolithic diets, but I can comment on their evolutionary underpinnings. From the standpoint of paleoecology, the Paleolithic diet is a myth. Food choice is as much about what’s available to be eaten as it is about what a species evolved to eat. And just as fruits ripen, leaves flush, and flowers bloom predictably at different times of the year, foods available to our ancestors varied over deep time as the world changed around them from warm and wet to cool and dry and back again. Those changes are what drove our evolution. Even if we could reconstruct the precise nutrient composition of foods eaten by a particular hominin species in the past (and we can’t), the information would be meaningless for planning a menu based on our ancestral diet.

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Because our world was ever changing, so too was the diet of our ancestors. Focusing on a single point in our evolution would be futile. We’re a work in progress. Hominins were spread over space too, and those living in the forest by the river surely had a different diet from their cousins on the lakeshore or the open savanna. What was the ancestral human diet? The question itself makes no sense. Consider some of the recent huntergatherers who have inspired Paleolithic diet enthusiasts. The Tikiġaġmiut of the north Alaskan coast lived almost entirely on the protein and fat of marine mammals and fish, while the Gwi San in Botswana’s Central Kalahari took something like 70 percent of their calories from carbohydrate-rich, sugary melons and starchy roots. Traditional human foragers managed to earn a living from the larger community of life that surrounded them in a remarkable variety of habitats, from near-polar latitudes to the tropics. Few other mammalian species can make that claim, and there is little doubt that dietary versatility has been key to the success we’ve had. --Originally published: Scientific American Online, April 2017.

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Mind over Meal: Weight-Loss Surgery and the Gut-Brain Connection by Bret Stetka For Teresa, the first plate of scrambled eggs was a transcendent experience. The 41-year-old Stanford University Medical Center nurse coordinator had completely lost her appetite in the days after her surgery. She ate, but only liquids and only at her surgeon’s request. Yet when her interest in eating returned, it was as though something about her relationship with food had fundamentally changed. The eggs, Teresa’s first solid meal in four weeks, were a revelation: simple, soft and buttery. To her surprise, they constituted a completely satisfying meal. Gone was the desire for sweets and excessively salted savories. Her once beloved french fries and rich desserts no longer enticed her. Her desire to eat was back, but for the first time in her life eating “right” came easy. Teresa had undergone a sleeve gastrectomy, one of a variety of procedures—known as bariatric surgeries—that manipulate the stomach and intestines to promote weight loss. Yet more than shedding pounds, which she did, it was the complete change in cravings that Teresa considers the most surprising result of her 2012 operation. She had struggled with her weight since childhood. Years of hormone therapy while trying to get pregnant did not help, nor did pregnancy itself. “Before I knew it, I was 270 pounds,” Teresa recalls. “And I just couldn’t get the extra weight off despite trying everything: every diet, lots of exercise.” The surplus pounds also made it hard to manage a toddler. “I couldn’t keep up with my son,” she says. A sleeve gastrectomy can shrink the stomach from the size of a football to that of a banana, roughly 15 percent of its original size. One year later—after months of eating healthier and eating less—Teresa was down to 150 pounds. “That was actually even low for me,” she says, “but the surgery really changed how I ate.” Since the 1960s, when these techniques were introduced, doctors have considered bariatric surgery primarily a mechanical fix. A smaller stomach, the reasoning went, simply cannot hold and process as much food. Patients get full faster, eat less and therefore lose weight. This idea is in part true. But now scientists know that it is not nearly that simple. Teresa’s weight loss was in all likelihood caused by the drastic change in how her gut speaks to her brain, and vice versa. The procedure had indirectly spurred new neural connections, changing how she thought about and craved food. Recent science has revealed that appetite, metabolism and weight are regulated through a complex dialogue between bowel and brain—one in which mechanical influences, hormones, bile acids and even the microbes living in our gut all interact with labyrinthine neurocircuitry. Bariatric surgery, scientists are discovering, engages and may change all these systems. In the process, it is helping researchers map how this complicated interplay manipulates our eating behaviors, cravings and frenzied search for calories during starvation. This work could also reveal new targets—including microbes and possibly the brain itself—that render the risky surgical procedure obsolete altogether. Brain Meets Bowel We have all felt the physical effects of the gut-brain communion: the gastric butterflies that come with love, the rumbles that arise before delivering a speech. These manifestations result from the brain signaling to the

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gastrointestinal tract, both through hormones and neuronal signals. Conversely, the gut can send signals back to the brain, too. In fact, coursing through our abdomen is the enteric nervous system, colloquially known as the second brain. This neural network helps to control food digestion and propulsion through the 30 feet of our gastrointestinal tract. It also communicates directly with the brain through the vagus nerve, which connects the brain with many of our major organs. Two primary gut-brain pathways regulate appetite. Both systems involve a small, central brain region called the hypothalamus, a hotbed of hormone production that helps to monitor numerous bodily processes. The first system comes into play during fasting. The stomach secretes the hormone ghrelin, which stimulates a region within the hypothalamus called the arcuate nucleus. This structure then releases neuropeptide Y, a neurotransmitter that, in turn, revs up appetite centers in the cerebral cortex, the outer folds of the brain, driving us to seek out food. In anticipation of mealtime, our brain sends a signal to the stomach via the vagus nerve, readying it for digestion. “This can occur simply at the sight, smell or thought of food,” says Mayo Clinic gastroenterologist and obesity expert Andres Acosta Cardenas. “Our brain is preparing our body for a meal.” The second gut-brain pathway suppresses our appetite. As we eat, several other hormones, including leptin and insulin, are secreted from fat tissue, the pancreas and the gastrointestinal tract. Separately, these hormones play many roles in digestion and metabolism. Acting together, they signal to another area of the hypothalamus that we are getting full. Our brain tells us to stop eating. The appetite and satiety loop constantly hums along. Yet hunger pathways also interact with brain regions such as the amygdala, involved in emotion, and the hippocampus, the brain’s memory center. Hence, our “gut feelings” and “comfort foods” are driven more by moods than mealtimes and nostalgic recollections of Grandma’s rhubarb pie. As a result of higher thinking processes, food now has context. Food is culture. As playwright George Bernard Shaw put it, “There is no sincerer love than the love of food.” Then there is the hedonistic thrill of sitting down to a meal. Eating also lights up our reward circuitry, pushing us to eat for pleasure independent of energy needs. It is this arm of the gut-brain axis that many scientists feel contributes to obesity. Neuroimaging work confirms that, much like sex, drugs, gambling and other vices, food can cause a surge of dopamine release in the brain’s reward circuitry. This neurotransmitter’s activity serves as a powerful motivator, one that can reinforce dining for its own sake rather than subsistence. Researchers have found that for rats, sweetness surpasses even cocaine in its desirability. In humans, psychiatrist Nora Volkow, director of the National Institute on Drug Abuse, has confirmed what chocolate lovers everywhere already know: food’s effects on the reward system can override fullness and motivate us to keep eating. Such findings hint at a neurobiological overlap between addiction and overeating, although whether eating can be an outright addiction remains a controversial question. The Surgical Solution Thanks to the flow of messenger hormones and neurotransmitters, our mind and stomach are in constant communication. Disrupting this conversation, as bariatric procedures must do, will therefore have consequences. Research has shown that in the days and weeks after bariatric surgery, sugary, fatty and salty foods become less palatable (as Teresa discovered). One study, published in 2010 by Louisiana State University neurobiologist HansRudolf Berthoud, found that rats lost their preference for a high-fat diet following gastric bypass surgery. In the 1990s multiple research teams had reported that after such surgery, patients often lose the desire to consume sweet and salty foods. More recently, a 2012 study by a team at Brown University found that adult patients had significantly reduced cravings for sweets and fast food following bariatric surgery. Similar findings in adolescent surgery patients also appeared in a 2015 study. The alteration in cravings and taste may be caused by changes in the release and reception of neurotransmitters throughout the gut-brain system. In 2016 Berthoud and his colleagues found that in the short term—around 10 days

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postprocedure—bariatric surgery in mice caused additional meal-induced neural activity in brain regions known to communicate with the gut compared with brain activity before the surgery. Specifically, the boost in activity was seen in a connection leading from stomach-sensing neurons in the brain stem to the lateral parabrachial nucleus, part of the brain’s reward system, as well as the amygdala. An expert in this area is biochemist Richard Palmiter of the University of Washington. In a 2013 study published in Nature, Palmiter’s group used complex genetic and cell-stimulation techniques—including optogenetics, a means of controlling living tissue using light—to activate or silence specific neurons in the brain stem parabrachial nucleus pathway in mice. He found that engaging this circuit strongly reduced food intake. But deactivating it left the brain insensitive to the cocktail of hormones that typically signaled satiety—such that mice would keep eating. Palmiter’s work suggests that engagement of the brain stem parabrachial pathway helps us curb our appetite. Because it is this same pathway that becomes unusually active postsurgery, it is probable that the hyperactivation Berthoud discovered is part of the gut-brain’s effort to assess satisfaction postsurgery. As he puts it, “the brain must relearn how to be satisfied with smaller portions.” In other words, bariatric surgery is certainly a mechanical change: with less space, the body needs to adjust. Still, there is clearly more to the story. After the procedure, more undigested food may reach the intestine, and, Berthoud speculates, it would then trigger a hormonal response that alerts the brain to reduce food intake. In the process, it would alter the brain’s activity in response to eating. If he is correct, the surgery’s success—at least in the short term—may have as much to do with its effects on the gut-brain axis as it does on the size of a person’s stomach. The Microbial Mind There is another player in the complex communications of mind and gut that might explain bariatric surgery’s effects. Experts have implicated the microbiota—the trillions of single-celled organisms bustling about our digestive system—in countless disorders, including many that affect the brain. Our co-denizens and their genome, the “microbiome,” are thought to contribute to autism, multiple sclerosis, depression and schizophrenia by communicating with the brain either indirectly via hormones and the immune system or directly through the vagus nerve. Research by gastroenterologist Lee Kaplan, director of the Massachusetts General Hospital Weight Center, suggests that the microbiota may play a role in obesity. In a study published in 2013 in Science Translational Medicine, Kaplan and his colleagues transferred the gut microbiota from mice that had undergone gastric bypass surgery to those that had not. Whereas the surgery group lost nearly 30 percent of their body weight, the transplanted mice lost a still significant 5 percent of their body weight. (Meanwhile a control group that did not have surgery experienced no significant weight change.) The fact that rodents could lose weight without surgery, simply by receiving microbes from their postoperative fellows, suggests that these microbial populations may be at least partly responsible for the effectiveness of bariatric procedures. A similar study, published in 2015 by biologist Fredrik Bäckhed of the University of Gothenburg in Sweden, found that two types of bariatric surgery—the Roux-en-Y gastric bypass and vertical banded gastroplasty— resulted in enduring changes in the human gut microbiota. These changes could be explained by multiple factors, including altered dietary patterns after surgery; acidity levels in the gastrointestinal tract; and the fact that the bypass procedure causes undigested food and bile (the swamp-green digestive fluid secreted by the liver) to enter the gut farther down the intestines. As part of the same research, Bäckhed and his colleagues fed mice microbiota samples from obese human patients who either had or had not undergone surgery. All the rodents gained varying degrees of body fat, but mice colonized with postsurgical microbiota samples gained 43 percent less. How might changes in our gut’s flora alter their interactions with the gut-brain axis and affect weight? Although the answer is still unclear, there are a few promising leads. Specific gut microbial populations can trigger hormonal and neuronal signaling to the brain such that they influence the development of neural circuits involved in motor control and anxiety. Bäckhed suspects gut flora

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after bariatric surgery could have a comparable effect on brain regions associated with cravings and appetite. The neurotransmitter serotonin could play a special role as well. About 90 percent of our body’s serotonin is produced in the gut, and in 2015 researchers at the California Institute of Technology reported that at least some of that production relies on microbes. Change the microbes; change the serotonin production. And that could make quite a difference because, as numerous studies have confirmed, stimulating the brain’s serotonin receptors can significantly reduce weight gain in rodents and humans. Treating the Gut-Brain Axis It is a welcome turn of fate that bariatric surgery is illuminating new directions in treating obesity—which affects more than 600 million people worldwide. Some of these avenues could render surgery obsolete or at least reserved for the most extreme cases. Thus, at the forefront of battling excess weight may be hijacking the gut-brain axis. In 2015, for example, the U.S. Food and Drug Administration approved a device that stimulates the vagus nerve to quell food cravings. A surgeon implants the device, made up of an electrical pulse generator and electrodes, in the abdomen so that it can deliver electric current to the vagus nerve. Although precisely how it works is unknown, the study leading to its approval found that patients treated for one year with this tool lost 8.5 percent more of their excess weight than those without the device. That approach offers some patients a less invasive alternative to bariatric surgery, but for the moment, vagus nerve stimulators are not as effective as many other obesity therapies. Meanwhile a number of intrepid neurosurgeons are investigating the use of a technique called deep-brain stimulation. Approved for use in Parkinson’s disease and obsessive-compulsive disorder, the procedure involves stimulating specific brain regions using implanted electrodes. Although this research is in its infancy, numerous brain regions involved in appetite control are being explored as possible targets. The Mayo Clinic’s Acosta Cardenas believes that in the future the best approach to treating obesity will be highly personalized. “Obesity is a disease of the gut-brain axis,” he says, “but I think we need to identify which part of the axis is abnormal in each patient to personalize treatment. I’m trying to identify which patients have a problem with the microbiome, or hormones, or emotional eating so we can maximize response to treatment.” In 2015 Acosta Cardenas and his colleagues looked at numerous factors potentially related to obesity in more than 500 normal-weight, overweight and obese patients. Among the factors were how quickly the study subjects got full, how quickly their stomachs emptied, hormone levels in response to eating and psychological traits. Acosta Cardenas’s findings support the idea that there are clear subclasses of obesity and that the cause and ideal treatment of obesity is most likely unique to each patient. For example, 14 percent of the obese individuals in his study have a behavioral or emotional component that would steer his treatment recommendation away from surgery and medication and toward behavioral therapy. He can also foresee a future in which he might prescribe a probiotic or antibiotic for obesity patients with an abnormal microbiota. At the moment there is no telling with certainty which perturbations of the gut-brain axis caused Teresa’s weight gain. But it is clear that she has benefited from surgery, maintaining her desired weight of 160 pounds for more than four years to date. Her feet do not hurt anymore. She has more energy. She can keep up with her son. And although she admits certain cravings have crept back during the years, they are not as intense as they once were and are far more manageable. “Before my surgery I had no self-control. I couldn’t hold back,” Teresa recalls. “Now if french fries show up at the dinner table, I may have a few, but I don’t have to deprive myself. I just don’t have the drive to eat that way anymore. I will inevitably take half of my meal home.” --Originally published: Scientific American MIND 28(4); 27-34 (July/August 2017).

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SECTION 2 Behavioral Intervention

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Don’t Diet! by Charlotte N. Markey My friend Ann (not her real name) recently tried the Paleo diet. She stopped eating dairy, grains, refined sugars and processed foods. Six weeks in, Ann had lost 15 pounds. But in that time, she had skipped happy hours, girls’ nights out, office parties—really any occasion that might have put her in arm’s reach of temptation. Ann missed her old life. She soon slid into her prediet habits and quickly gained back the pounds, plus a few more—a familiar experience for her. Ann has lost weight on many diets, but she can never maintain the regimen for long. After she quits, the scale, like a pendulum, always swings back up. Her predicament is not unusual. At any given time, at least one in five American adults reports being on a diet, but the majority don’t keep the weight off. A huge amount of scientific evidence tells us that dieting does not promote lasting weight loss. In fact, many dieters end up gaining back more weight after they quit. When I say “diet,” I am referring to eating regimens that require cutting portions, severely restricting calories, or eliminating entire food groups: carbs, fats, sweets, whatever. Despite such deprivations, diets remain alluring because they offer a clear and quick prescription dictating what you should and should not eat. These tactics are meant to tame erratic eating behaviors and revise poor food choices. But the truth is that such strategies hardly ever work because they are too extreme and thus almost impossible to maintain over the long term. My advice as a psychologist and researcher who focuses on weight control: Do not diet. Do not cut out groups of foods or count calories. Do not try to eat very little or deprive yourself. Such strategies backfire because of psychological effects that every dieter is all too familiar with: intense cravings for foods you have eliminated, bingeing on junk food after falling off the wagon, an intense preoccupation with food. A growing body of research shows why these tendencies undermine most people’s diet efforts and confirms that the way around these pitfalls is moderation. Making small changes to your eating patterns, ones you can build on slowly over time, is truly the best pathway to lasting weight loss. Although you may have heard this message of moderation before, the evidence is finally too overwhelming to ignore. Effective weight management is particularly important when we consider that two thirds of Americans older than 20 are overweight or obese. With the rise in obesity rates and related health problems, such as diabetes and heart disease—both of which are leading causes of death in the U.S.—it has become even more critical for us all to approach weight loss armed with a keen understanding of what really works and what doesn’t. Let’s start with what doesn’t. Why Typical Diets Fail The “what the hell effect”: Studies have consistently revealed that dieting usually leads to weight gain, not weight loss. In a 2013 review published online in Frontiers in Psychology, investigators reported that 15 of 20 studies showed that dieting predicted weight gain in adolescents and adults of normal weight. One problem with diets is that once you give into temptation after restricting yourself, you are more likely to binge. This tendency, which psychologists dub the “what the hell effect,” undermines attempts to lose weight. A 2010 study by psychologists at the University of Toronto demonstrated this effect in people who believed they had broken their diet. In the study, 106 female students—some of whom were dieting and some of whom were not—all

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received identical slices of pizza. Some of the students saw a person carrying another slice that was either bigger or smaller than the one they got, and others did not see another slice. After they ate the pizza, the participants were asked to taste-test a range of cookies. Women who weren’t dieting and dieters who thought they had eaten a smaller than usual slice or who didn’t see a comparison slice ate a small amount of cookies. But dieters who thought they had violated their diet by eating a bigger slice ate more cookies than everyone else. The researchers suggest that these women believed they had already blown their diet—so what the hell, might as well pig out on cookies. This study and many others like it confirm that violating or even thinking you have gone off your diet is enough to abandon self-control. Ironic processing: Some diets promise you’ll avoid feelings of deprivation by letting you eat as much as you want of certain food groups while totally eliminating others. The trouble is that when you eliminate your favorite foods—a requirement of most weight-loss regimens—you develop a deeper longing for them. Vow to avoid pasta, and you will soon find yourself dreaming about spaghetti. Food preoccupation is an inevitable result of dieting. Psychologists call this phenomenon “ironic processing”— suppressing a thought makes it more salient. It became famous when the late social psychologist Daniel M. Wegner did a series of experiments—the white bear studies—in which he asked subjects to avoid all thoughts of a white bear. Guess what creature relentlessly prowled through their minds! Many studies over the years have shown that people who try to eliminate food groups end up craving those foods intensely. One published this year confirms that finding and adds to mounting evidence that not only do people crave the forbidden food, they eat more of it when they get a chance. The study compared eating patterns in 23 normal-weight nondieters who restricted their intake of palatable foods, such as doughnuts and ice cream, and 23 similar people who merely recorded their snack intake. The researchers found that participants who restricted themselves reported craving and eating more treats, whereas those who simply monitored their snacks did not. This growing line of research suggests that for most, eliminating foods entirely will backfire badly. In fact, treating yourself to indulgences may help you avoid the pitfalls of craving and overeating forbidden foods. In a 2012 study, 144 obese men and women were put on a strict, low-calorie diet for 16 weeks. About half ate a regular breakfast—300 calories—and the rest consumed a larger breakfast—600 calories—which included something sweet, such as a doughnut or chocolate (and ate less at dinner to make up for it). In the second half of the study, participants tried to maintain their meal plans on their own for 16 more weeks. The participants kept food diaries and continued to receive counseling from a dietitian. After the initial 16 weeks of close monitoring, the small breakfast group had lost a few more pounds than the large breakfast group (33 versus 30 pounds). But in the self-maintenance 16-week period, the small breakfast group regained 25 pounds, whereas the large breakfast group continued to shrink, dropping 15 additional pounds. Notably the small breakfast group reported increased cravings for sweets, fats and fast foods at the end of the study, whereas the large breakfast group reported reduced cravings in each category. Although eating dessert for breakfast is not necessarily the fastest or healthiest route to weight loss, these findings demonstrate that it is possible to have your cake and lose weight, too. Mental fatigue: Although efforts to change your eating behaviors require attention and record keeping, especially at the beginning, focusing too much energy on what you eat reduces your ability to do other, potentially more important things. Studies that examine the mental energy available to dieters versus nondieters consistently reveal that dieters have more difficulty learning new information, solving problems and exerting self-control. Overthinking your food choices may also have deleterious consequences for your mental health. A 2010 study in Appetite looked at the mental toll of eating chocolate among dieters and nondieters. The nondieters were not particularly distracted by this indulgence, but the dieters could no longer think clearly, becoming consumed with thoughts, such as “Why did I eat that?” and “What should I eat later today to make up for eating that?’ Another experiment published in 2010 found that women who restricted their caloric intake and recorded what they ate exhibited elevated cortisol levels, a marker of biological stress. Even women who simply monitored their meals without trying to restrict calories reported feeling more stressed, and they ended up gaining weight. The

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bottom line is, for most people, that diets not only backfire, they also take a heavy toll on our physical and mental well-being. What You Should Do Start with your head: If you want to improve your body, you must also improve your mind-set. Decades of research show that individuals who are dissatisfied with their bodies are less successful at losing weight. Studies also show that it is possible for anyone to learn to feel good about his or her body. In a 2014 study, women with eating disorders, including some who binged or who were overweight, received compassion-focused therapy—an approach aimed at reducing feelings of shame and improving self-esteem. Over the 12-week treatment, women who exhibited greater improvements in self-compassion and reductions in body shame were also more likely to develop better eating habits. One simple way to improve your self-esteem, according to many findings, is to write positive affirmations on a regular basis. Happiness research has consistently shown that focusing on what you do like—“I have nice eyes”— and on health rather than appearance-related goals—“I want to run a 5K this year”—can help you develop a healthier mind-set and self-image. Simple, slow and steady: When setting a weight loss goal, it is natural to want to accomplish it immediately. Yesterday! But to maintain a more svelte figure, you need to make gradual, sustainable changes to your diet: for example, drinking less alcohol and juice, substituting diet soda or seltzer for regular soda, and eating dessert on four nights a week instead of seven. Making even small changes such as these may sound like a “diet,” which I have told you to avoid, but it is not, for one important reason: this slow, steady approach allows you to adjust to a new routine at your own pace without the intense effort and denial that typical diet plans require. Most people trying to lose five to 50 pounds will benefit from this slow-to-moderate approach to weight loss, but it is important to note that individuals whose health is at serious risk because of obesity will likely need more drastic measures and should consult a physician. A large body of research supports the idea that making simple, gradual changes to your eating patterns is the best way to promote lasting weight loss. Robust evidence for this approach comes from a 2008 study, which demonstrated that overweight and obese adults who made very modest changes to their daily calorie intake and physical activity levels lost four times more weight than those following regimens that involved more extreme calorie restriction. The moderate group lost 10 pounds in one month, and they sustained the weight loss over the next three months. In support of this approach, a 2015 study published in PLOS ONE found that women who successfully modified their diet and exercise habits over time set small, achievable behavior change goals, had realistic expectations about their weight loss and were internally motivated to lose weight. The women who relapsed or failed to change their habits tended to have unrealistic expectations, lower motivation and self-confidence, and less satisfaction with their progress. Some of the most compelling data on effective weight-loss strategies comes from the National Weight Control Registry (NWCR), which surveyed more than 4,000 people who lost at least 30 pounds and kept it off for at least a year. The best tactics, according to the seminal 2006 report, included self-monitoring, such as limiting certain foods, keeping track of portion sizes and calories, planning meals and incorporating exercise into the daily routine. Such advice may appear to conflict with the research I described earlier on the pitfalls of restriction and mental fatigue, but the truth is, to lose weight, it is important to find the right balance. For instance, before making changes to your diet, you need to understand your current eating patterns, which may require considerable thought and attention. Most overweight individuals, when they are not trying to diet, tend to eat erratically—consuming junk food, snacking a lot and indulging cravings on a whim. Becoming aware of these habits, the good and bad, will allow you to tailor them. As you begin to make small tweaks to your daily eating, start to plan a few meals you like that you can cycle through on a regular basis, so you don’t have to think too hard about what you’re going to eat every day.

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According to the NWCR data, people who plan their meals are 1.5 times more likely to maintain their weight loss. The NWCR data also show that limiting the variety of foods you eat can help you sustain your weight. You don’t have to eat the same foods every day, but generally reducing the array of options makes grocery shopping less stressful. Work it out: We all know by now that exercise is essential for all-around health. Yet study after study shows that working out is not terribly effective for weight loss on its own. When combined with better eating habits, however, exercise appears to help people slim down. A 2012 study looked at the effects of diet or exercise, or both or neither, in a group of overweight or obese postmenopausal women. Dieters could consume between 1,200 to 2,000 calories a day, depending on their initial weight, and exercisers ramped up to 45 minutes or more of cardio five days a week. After 12 months, those in the combined diet and exercise group lost the most weight—about 19.5 pounds—although the diet-only group was not far behind, losing 15.8 pounds. Those who only exercised lost 4.4 pounds, and the control group, who didn’t exercise or eat differently, lost 1.5 pounds over the year. Once your goal weight is achieved, exercise may be crucial for keeping the scale steady. Most people who have slimmed down report that routine physical activity is an important part of their maintenance regimen. Exercise has many physiological benefits; it even appears to moderate the brain’s reaction to pleasurable foods. In a small 2012 study, overweight or obese participants underwent an initial brain scan while looking at images of food. Then they were put on a six-month exercise regimen. At six months, the exercisers showed decreased activity in the insula, which regulates emotions, in response to images of palatable treats. They did not, however, report changes in dietary restraint, food cravings or hunger, suggesting that the neural effects are subtle—perhaps helpful during weight maintenance but not strong enough to induce weight loss. Incorporating exercise into your life should be a gradual process. You don’t have to run marathons to reap psychological and physical rewards. Going for a lunchtime walk or biking to work is a way to integrate activity into your daily routine. You can also increase your movements in small ways by taking the stairs instead of riding the elevator or washing your car instead of driving through the car wash. Being disciplined is important, but making exercise fun and sustainable is also essential. Don’t do it alone: Receiving social support is key to losing weight. Consulting a physician or nutritionist is one way to elicit support and provide greater accountability. Research also demonstrates the role romantic partners play in encouraging weight loss. In my work, I have found that men are better able to adopt and stick with healthier eating habits when they receive support and encouragement from their spouse. Similarly, friends, co-workers and online weight-loss buddies can keep you on track by offering inspiration, praise and partners in crime. More systematic help has been shown to be useful, too, such as becoming a member of Weight Watchers or other support groups or participating in the community of users of smartphone apps such as MyFitnessPal, Lose It! or SmartenFit (the last of which I co-developed). After decades of diet studies, we can no longer ignore the fact that the preponderance of evidence points toward these small, sustainable steps as the best way to lose weight. That message may not be as sexy or exciting as the latest fad diet, but the science is clear: moderation leads to changes that will last for the rest of your life. Creating good habits takes time, patience and resolve, and you will inevitably encounter setbacks along the way. But the key is to never give up—and in a few short months, you may find yourself on the road to the body and active way of life you’ve always dreamed about. Weighing In on Popular Diets The small, moderate changes I recommend in this article are the best way to lose weight over the long term, but the allure of popular diets remains strong. A small percentage of people do find long-term success on these diets, so it is hard to discount such strategies entirely—although the evidence suggests that a moderate approach will give you better odds of meeting your goals. Here’s the lowdown on a few popular diets:

PALEO The Plan: Based on the premise that we’d be better off eating as our hunter-gather ancestors did, the Paleo diet prescribes a diet of veggies, fruits, meat and nuts; it eliminates dairy, whole grains, refined sugars, processed foods and legumes.

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The Skinny: Our current food environment is not compatible with that of our ancestors. Eating as the Paleo diet dictates is unrealistic long term because it is so restrictive, making an enjoyable social life almost impossible. Cutting out so many food groups leads to distressing cravings for most people, too. ATKINS The Plan: The diet calls for high quantities of protein and very limited carbohydrate and sugar intake. Doing this increases our ability to burn fat. The Skinny: Many studies show that this strategy works well for weight loss in the short term, but most people end up gaining back the weight over time. Such results are a good example of how extreme restriction tends to backfire. 5:2 FAST DIET The Plan: Eat normally for five days a week and fast for two, with women allowed 500 calories and men allowed 600 on fast days. The Skinny: The 5:2 diet has received a lot of recent attention. Preliminary evidence in humans and in mice suggests that it may aid weight loss, but the jury is still out. The main problem is that 500 or 600 calories will likely leave you unsatisfied at the end of the day. If you’re hungry, you’re going to crave food, especially energydense treats, more so than if you ate moderately. Once you give into your hunger, the “what the hell effect” will likely set in. WEIGHT WATCHERS The Plan: Weight Watchers emphasizes making healthy and sustainable lifestyle changes by consuming balanced meals. The plan highlights fruits and vegetables, and the meals can be tailored to an individual’s likes. No foods are off-limits. The Skinny: Weight Watchers does a lot of things right. From a nutritional and psychological standpoint, the recommendations to enlist peer support and not to eliminate particular food groups agree with the advice I offer. Some people, however, may find the cost prohibitive—there are registration and weekly fees—and research suggests that weekly weigh-ins can be counterproductive, making some dieters distraught if the scale doesn’t match their expectations. —C.N.M. --Originally published: Scientific American MIND 26(5); 46-52 (September/October 2015).

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Behavior: The Additional Key to Weight-Loss by David H. Freedman Obesity is a national health crisis–that much we know. If current trends continue, it will soon surpass smoking in the U.S. as the biggest single factor in early death, reduced quality of life and increased health care costs. A third of adults in the U.S. are obese, according to the Centers for Disease Control and Prevention, and another third are overweight, with Americans getting fatter every year. Obesity is responsible for more than 160,000 “excess” deaths a year, according to a study in the Journal of the American Medical Association. The average obese person costs society more than $7,000 a year in lost productivity and extra medical treatment, say researchers at George Washington University. Lifetime-added medical costs alone for a person 70 pounds or more overweight amount to as much as $30,000, depending on race and gender. All this lends urgency to the question: Why are extra pounds so difficult to shed and keep off? It does not seem as though it should be so hard. The basic formula for weight loss is simple and widely known: consume fewer calories than you expend. And yet if it really were easy, obesity would not be the nation’s number-one lifestylerelated health concern. For a species that evolved to consume energy-dense foods in an environment where famine was a constant threat, losing weight and staying trimmer in a modern world of plenty fueled by marketing messages and cheap empty calories is, in fact, terrifically difficult. Almost everybody who tries to diet seems to fail in the long run—a review in 2007 by the American Psychological Association of 31 diet studies found that as many as two thirds of dieters end up two years later weighing more than they did before their diet. Science has trained its big guns on the problem. The National Institutes of Health has been spending more than $800 million a year on studies to understand the metabolic, genetic and neurological foundations of obesity. In its strategic plan for funding obesity research, published in 2011, the NIH placed at the top of the list of research opportunities the investigation of basic biological processes related to obesity, including “specific roles of organs, tissues, and molecules in the development of obesity” and “genes, epigenetics, and critical periods in human development.” This research has provided important insights into the ways proteins interact in our body to extract and distribute energy from food and produce and store fat; how our brain tells us we are hungry; why some of us seem to have been born more likely to be obese than others; and whether exposure to certain foods and toxic substances might modify and mitigate some of these factors. The work has also given pharmaceutical companies numerous potential targets for drug development. What the research has not done, unfortunately, is make a dent in solving the national epidemic. Maybe someday biology will provide us with a pill that re adjusts our metabolism so we burn more calories or resets our built-in cravings so we prefer broccoli to burgers. But until then, the best approach may simply be to build on reliable behavioral-psychology methods developed over 50 years and proved to work in hundreds of studies. These tried-and-true techniques, which are being refined with new research that should make them more effective with a wider range of individuals, are gaining attention. As the NIH puts it in its proposed strategic plan for obesity research: “Research findings are yielding new and important insights about social and behavioral factors that influence diet, physical activity, and sedentary behavior.” The Biology of Obesity

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The National Institutes of Health has spent more than $800 million a year on studies to understand the neurological, metabolic and genetic foundations of obesity. In the process, scientists have uncovered complex biochemical pathways and feedback loops that connect the brain and digestive system; a new appreciation for the regulatory functions of fat tissues; subtle hereditary changes that make some groups more prone to obesity than others; and the strong possibility that exposure to certain foods and toxic substances might modify and mitigate some of these factors. Given that it will likely take decades to understand the various causes of obesity, more surprises are no doubt in store.

Credit: Illustration by Peter and Maria Hoey.

How We Got Here The desperation of the obese and overweight is reflected in the steady stream of advice pouring daily from sources as disparate as peer-reviewed scientific journals, best-selling books, newspapers and blogs. Our appetite for any diet twist or gimmick that will take the pounds off quickly and for good seems to be as insatiable as our appetite for the rich food that puts the pounds on. We, the public, love to believe in neat fixes, and the media oblige by playing up new scientific findings in headline after headline as if they are solutions. It does not help that the scientific findings on which these headlines are based sometimes appear to conflict. For example, a 2010 study in the American Journal of Clinical Nutrition linked weight loss to increased dairy intake, although a 2008 meta-analysis in Nutrition Reviews found no such link. A 2010 paper in the Journal of Occupational and Environmental Medicine postulated a connection between job stress and obesity, but another report that year in the journal Obesity concluded the two are uncorrelated. Part of the problem is that obesity researchers are in some ways akin to the metaphorical blind men groping at different parts of the elephant: their individual study findings address only narrow pieces of a complex puzzle. When the research is taken together, it is clear that the obesity fix cannot be boiled down to eating certain kinds of food or taking other simple actions. Many factors contribute to the problem. Some are environmental—the eating habits of your friends, what food is most available in your home and your local stores, how much opportunity you have to move around at work. Others are biological, such as genetic predispositions for storing fat,

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having higher satiety thresholds or having more sensitive taste buds. Economics and marketing play roles, too. Junk food is much cheaper than fresh produce. And food companies are masters at manipulating our social nature and our evolutionary “programming” to steer us toward unhealthy but profitable fare. That is why the narrow “eat this” kinds of solutions, like all simple solutions, fail. When we go on diets and exercise regimens, we rely on willpower to overcome all these pushes to overeat relative to our activity level. And we count on the reward of getting trimmer and fitter to keep us on the wagon. It is rewarding to lose the weight, of course. Unfortunately, time works against us. As the weight comes off, we get hungrier and develop stronger cravings and become more annoyed by the exercise. Meanwhile the weight loss inevitably slows as our metabolism tries to compensate for this deprivation by becoming more parsimonious with calories. Thus, the punishment for sticking to our regimen becomes increasingly severe and constant, and the expected reward recedes into the future. “That gap between the reinforcement of eating and the reinforcement of maybe losing weight months later is a huge challenge,” says SungWoo Kahng, a neurobehaviorist who studies obesity at the University of Missouri. We would be more likely to stick with the regimen if it remained less punishing and more reliably rewarding. Is there a way to make that happen? From Biology to Brain The most successful way to date to lose at least modest amounts of weight and keep it off with diet and exercise employs programs that focus on changing behavior. The behavioral approach, tested over decades, involves making many small, sustainable adjustments in eating and exercise habits that are prompted and encouraged by the people and the rest of the environment around us. The research in support of behavioral weight-loss approaches extends back more than half a century to Harvard University psychologist B. F. Skinner’s development of the science of behavioral analysis. The field is founded on the notion that scientists cannot really know what is going on inside a person’s brain—after all, even functional MRIs, the state of the art for peering into the mind, are crude, highly interpretable proxies for cognition and emotion that reduce the detailed firing of billions of neurons in complex circuits to a few blobs of color. But researchers can objectively and reproducibly observe and measure physical behavior and the immediate environment in which the behavior occurs, allowing them to identify links between environment and behavior. That typically includes trying to spot events or situations that may be prompting or triggering certain behaviors and noting what may be rewarding and thus reinforcing of some behaviors or punishing and thus inhibiting of others. The effectiveness of behavioral interventions has been extensively documented for many disorders and problem behaviors. A 2009 meta-analysis in the Journal of Clinical Child & Adolescent Psychology concluded that “early intensive behavioral intervention should be an intervention of choice for children with autism.” A systematic review sponsored by the U.S. Preventive Services Task Force concluded that even brief behavioral-counseling interventions reduced the number of drinks taken by problem drinkers by 13 to 34 percent for as long as four years. Studies have found behavioral-intervention successes in challenges as diverse as reducing stuttering, increasing athletic performance and improving employee productivity. To combat obesity, behavioral analysts examine related environmental influences. Which external factors prompt people to overeat or to eat junk food, and which tend to encourage healthful eating? In what situations are the behaviors and comments of others affecting unhealthful eating? What seems to effectively reward eating healthfully over the long term? What reinforces being active? Behaviorally focused studies of obesity and diets as early as the 1960s recognized some basic conditions that seemed correlated with a greater chance of losing weight and keeping it off : rigorously measuring and recording calories, exercise and weight; making modest, gradual changes rather than severe ones; eating balanced diets that go easy on fats and sugar rather than dropping major food groups; setting clear, modest goals; focusing on lifelong habits rather than short-term diets; and especially attending groups where dieters could receive encouragement to stick with their efforts and praise for having done so. If these strategies today sound like well-worn, commonsense advice, it is because they have been popularized since 1963 by Weight Watchers, which was founded to provide support groups for dieters. Weight Watchers later

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added other approaches and advice in keeping with the findings of behavioral studies and billed itself as a “behavior-modification” program. “Whatever the details are of how you lose weight, the magic in the sauce is always going to be changing behavior,” says Karen Miller-Kovach, former chief science officer of Weight Watchers. “Doing that is a learnable skill.” Studies back the behavioral approach to weight loss. A 2003 review commissioned by the U.S. Department of Health and Human Services found that “counseling and behavioral interventions showed small to moderate degrees of weight loss sustained over at least one year”—a year being an eon in the world of weight loss. An analysis of eight popular weight-loss programs published in 2005 in the Annals of Internal Medicine found Weight Watchers (then in its pre-2010 points-overhaul incarnation) to be the only effective program, enabling an average reduction of 3 percent body weight maintained for the two years of the study. Meanwhile a 2005 JAMA study found that Weight Watchers, along with the Zone diet (which similarly recommends a balanced diet of protein, carbohydrates and fat), achieved the highest percentage (65 percent) of one-year diet adherence among several popular diets, noting that “adherence level rather than diet type was the key determinant of clinical benefits.” A 2010 study in the Journal of Pediatrics found that overweight children receiving one year of behavioral therapy dropped 1.9 to 3.3 units more in body mass index, a height-weight relation correlated to body fat, than control subjects did. The Pediatrics report noted that “more limited evidence suggests that these improvements can be maintained over the 12 months after the end of treatments.” A 2010 study in Obesity found that continuing members of Take Off Pounds Sensibly (TOPS), a national, nonprofit, behaviorally focused weight-loss organization, maintained a weight loss of 5 to 7 percent of their body weight for the three years of the investigation. The U.K.’s Medical Research Council declared in 2010 that its own long-term study had shown that programs based on behavioral principles are more likely to help people take and keep the weight off than other approaches. (The study was funded by Weight Watchers, but without its participation.) Weight Watchers and other widely marketed programs tend to fall short, however, in enlisting a full range of behavioral techniques and customizing them to meet the varied needs of individuals. They do not routinely provide individual counseling, adapt their advice to specific challenges, assess environmental factors in a member’s home, workplace or community, provide much outreach to members who do not come to meetings, or prevent their members from shooting for fast, dramatic, short-term weight loss or from restricting food groups. In search of profits, Weight Watchers sometimes even mildly panders to these self-defeating notions in its marketing. “Some people join us to drop 10 pounds for a high school reunion,” Miller- Kovach says. “They achieve that goal, then stop coming.” To close that gap, a number of researchers have turned their attention in recent years to improving, expanding and tailoring behavioral techniques, with encouraging results. For example, Michael Cameron, chief clinical officer of Pacific Child & Family Associates, a national group of clinics for children with special needs, has authored more than 20 articles in peer-reviewed journals documenting the effectiveness of a wide range of behavioral interventions. A former faculty member at Harvard Medical School’s teaching psychiatric hospital, Cameron in 2011 conducted a yearlong, four-person study—behavioral analysts generally do very small group or even singlesubject studies to more closely tailor the intervention and observe individual effects—in which the subjects met together with him via online video-conferencing for reinforcement, weighed themselves on scales that transmitted results via wireless networks, and had their diets optimized to both reduce caloric density and address individual food preferences. Favorite foods were used as a reward for exercise. The subjects lost 8 to 20 percent of their body weight, and Cameron says they and the several other people he has worked with outside the study have all kept the weight off. Matt Normand, a behavioral analyst at the University of the Pacific, has investigated ways to more precisely track subjects’ calorie intake and expenditure. He collects receipts of their food purchases, provides checklists to record what they eat, and uses pedometers and other devices to measure their physical activity. He then gives participants daily detailed accounts of their calorie flow. In one published study, Normand showed that three of four subjects reduced calorie intake to recommended levels. Richard Fleming, a researcher at the University of Massachusetts Medical School’s Shriver Center, has in Obesity looked at ways to encourage parents to steer their children to healthier choices. He has found, among other

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techniques, that showing parents in person what appropriate serving sizes of foods look like on plates is helpful. Another successful Fleming trick: letting children pick out a small treat at a food store—as long as they walk there. “Kids can really respond to that reward for being active,” he says. Why are behavioral interventions effective? Laurette Dubé, a lifestyle psychology and marketing researcher at McGill University’s Faculty of Management, notes that our environment is currently one in which ubiquitous, sophisticated marketing efforts prey on our need for sensory gratification as well as our vulnerability to misinformation. In addition, the poor eating and exercise habits we observe in our friends, family and colleagues encourage us to follow suit. In essence, behavioral interventions seek to reconfigure this environment into one in which our needs for information, gratification and social encouragement are tapped to pull us toward healthy food and exercise choices rather than away from them. “When we are getting the right messages in enough ways, we have a better chance of resisting the urge to eat more than we need,” Dubé says. Changing Policy There is no one-size-fits-all solution, behavioral or otherwise, to the problem of obesity. But although behavioral interventions work best when they are customized to individuals, mass-market behavioral approaches such as TOPS and Weight Watchers are at least fairly effective. Why don’t more people lose weight with them? The main reason is that people simply do not sign up for them, often because would-be weight losers are chasing fad diets or supplements or have read that obesity is locked into our genes. Weight Watchers, by far the most popular behavioral weight-loss program, counts only 600,000 meeting-attending members in its ranks in North America. That means that in the U.S., fewer than one out of 100 obese people and about one out of 200 overweight people are part of a formal behavioral-modification program. Public policy may be changing, however. The U.S. Surgeon General’s office and the CDC have both publicly lined up behind behavioral approaches as the main weapon in what is becoming a war on obesity. First Lady Michelle Obama’s Let’s Move campaign against childhood obesity consists almost entirely of finding ways to encourage children to eat lower-calorie foods, to become more active, and to enjoy doing it. San Francisco’s 2010 ban of free toys in fast-food meals for kids suggests that more officials may be ready to pressure the food industry into easing up on what are essentially obesity-supportive marketing tactics. To encourage people in poorer, disproportionately over weight communities to buy healthier food, the White House has proposed subsidizing the costs of fruits and vegetables. Approaching the problem from the other direction, former New York City mayor Michael Bloomberg advocated modifying food-assistance programs to restrict the purchase of high-sugar beverages and supported a ban, passed by the city’s board of health, on extra-large servings of sugary sodas. In 2014 voters in Berkeley, Calif., approved a surtax of 1 cent per ounce on such drinks. New York City has also offered vouchers for buying produce at farmers’ markets to low-income families and incentives to stores to offer healthier fare. Increasing access to behavior therapy would help, too. Many overweight people might need only online behavioral monitoring, support and progress-sharing tools, which have proved moderately effective in studies. Others may need much more intensive, more personal interventions of the kind Cameron is developing. Given that obesity especially plagues the economically disadvantaged, fees for these programs may have to be heavily subsidized by the government and health care insurers. A weekly session with a behavioral therapist costing $50 would amount to $2,500 a year, or a bit more than a third of the $7,000 a year societal and medical costs of obesity —and the sessions might be needed for only a year or two to establish new, permanent eating and exercise habits, whereas the savings would continue on for a lifetime. It is too soon to say whether the public will accept government efforts to push it toward healthier choices. San Francisco’s ban on Happy Meal toys was initially vetoed by the mayor in response to angry reaction. Efforts by Let’s Move to bring healthier food to school cafeterias have been intensely criticized by some as overly intrusive. The courts threw out New York City’s ban on large sodas. And voters have rejected taxes on high-calorie beverages in San Francisco and most other cities and states that have proposed them. Even if such efforts are eventually fully implemented nationwide, there is no way of being sure they will significantly reduce obesity. The current rate of obesity is far beyond any ever seen before on the planet, and thus a

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large-scale solution will necessarily be an experiment in mass behavior change. But the research suggests that such a grand experiment would be our best shot at fixing obesity and that there is reason to be hopeful it will succeed. Given that more and more scientists, public policy experts and government officials seem eager to get it off the ground, we may well have early findings within this decade.

Credit: Illustration by Peter and Maria Hoey.

--Originally published: Scientific American 304(2); 40-47 (February 2011).

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SECTION 3 Mental Floss: Your Brain on Exercise

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Head Strong by Ferris Jabr On Valentine’s Day 2014 Elizabeth Droge-Young admitted herself to a hospital in Syracuse, N.Y. For more than a year, she had been struggling with depression—not eating well and losing interest in the movies, books and music that usually delighted her. She had withdrawn from her friends and was routinely missing classes at Syracuse University, where she was a fifth-year graduate student in evolutionary biology. Some days that winter she could not even make it out of bed, despite the fact that she had started taking antidepressants the previous fall. In her darkest moments, obsessive and frightening thoughts of self-harm and suicide flooded her mind. “It was horrible,” she recalls. “I felt very unsafe.” She realized she needed a serious intervention. After a week and a half on suicide watch at the hospital, plus a stronger cocktail of medications, Droge-Young returned home, taking an academic leave of absence for the remainder of the school year. For a while, she seemed to be getting better. But when she went back to school in August, the unbearable sadness and dark impulses resurfaced. This time she turned to a hospital in Saratoga Springs, N.Y., some two and a half hours away, which offered a more holistic treatment. In addition to medication and counseling, her doctors prescribed a full schedule of daily activities, such as arts and crafts and walks around the grounds. During her stay, a hospital therapist also recommended exercise. So after her release, Droge-Young started going to the gym three to five times a week, walking and jogging on the treadmill, lifting weights and attending Zumba, a popular dance fitness class. “It was empowering,” says Droge-Young, now 33 and working as a freelance science writer in Providence, R.I. “It really helped with my mood. There’s something wonderful about the mind-body connection exercise provides. Using weight machines or jogging on the treadmill allows you to be self-reflective: ‘Look at the strength and endurance I have. This is something positive about myself.’ And the dancing was joyful—just being able to move around in a way that was free and felt good.” Since incorporating exercise into her regimen for managing depression, Droge-Young has never relapsed to the point of requiring another hospitalization. To this day, she considers dance and riding on a stationary bike to be a crucial component of her treatment. The fact that exercise improves physical health is so well known as to be a platitude. Decades of research demonstrate that regular exercise lowers the risk of many illnesses—heart disease, obesity, diabetes, cancer—and extends the average life span. In contrast, the benefits of exercise for mental health are not quite so obvious or well publicized. We work out to “get in shape,” and some of us depend on bike rides, neighborhood jogs or yoga to help clear our mind and relieve stress. But how often do we seriously consider exercise as a viable treatment for mental illness, one just as effective as medication or counseling? Can a steady routine of physical workouts really help to keep psychological disorders in check? In the case of depression, the collective evidence to date suggests that the answer is an emphatic yes. Exercise is by no means a panacea, and in severe cases of depression, it may be futile on its own. But scores of experiments now show that exercise is much more than a temporary distraction from mental woes or some ultimately inconsequential palliative. It appears to combat depression in a number of ways: by strengthening our biochemical resilience to stress, encouraging the growth of new brain cells, bolstering self-esteem and possibly even counterbalancing an underlying genetic risk for mental illness. For most people with mild to moderate depression, exercise is one of the strongest, safest, most practical, most affordable and even enjoyable treatments available. “I am a big believer in the value of physical activity,” says clinical psychologist James Blumenthal of Duke University. “The majority of evidence suggests that a certain subset of patients can benefit just as much with

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exercise, if not more, than with medication.” Psychiatrist Madhukar Trivedi of the University of Texas Southwestern Medical Center, who has studied the relation between exercise and mental health for more than 15 years, agrees: “We have now generated a whole big body of literature about exercise as a treatment for depression. We’ve looked at dose, at adding exercise as an augmentation treatment, at specific biomarkers associated with improvement. We have the studies to show that something really powerful and interesting is going on.” On the Strength of the Evidence Major depression—an illness characterized by a persistent low mood or loss of interest in typically pleasurable activities, often accompanied by insomnia, fatigue, poor concentration or feelings of worthlessness—is one of the leading causes of disability and death around the globe, according to the World Health Organization. At any given time, it afflicts around 350 million people worldwide and 18 million people in the U.S. Only a fraction of sufferers seek help, and of those, only a third respond to standard treatment, which is usually counseling and medication. Antidepressant drugs are often costly and can have serious side effects, driving many patients to search for less expensive, safer, more natural solutions. In a survey of more than 2,000 U.S. adults published in 2001, more than half of the respondents with depression said that they had turned to some kind of alternative treatment, such as yoga, herbal medicines or acupuncture. Psychologists and clinicians have studied exercise as an alternative treatment for depression for at least 30 years. Blumenthal was one of the pioneers. In the 1980s, while researching how exercise helps patients with cardiovascular disease, he and his colleagues noticed an inadvertent secondary benefit: working out seemed to improve people’s moods and reduce symptoms of depression. They decided to investigate. One of their early studies, published in 1999, tracked the health of 156 elderly men and women diagnosed with depression as they exercised regularly or took antidepressants, or both. After 16 weeks, all three groups had improved equally, but relapse rates were lowest among patients who exercised. In a follow-up study, published a decade later, they divided more than 200 adults with depression into four groups, each receiving a different intervention: supervised exercise classes, exercise at home, medication or placebo. They found that patients engaging in supervised exercise fared better than those working out at home and achieved nearly equivalent remission rates as those taking antidepressants: 45 versus 47 percent, respectively. By comparison, the home exercise group reached a 40 percent remission rate and the placebo group, 31 percent. More recently, in a similar study in 2015, Swedish scientists assigned 946 patients with mild to moderate depression to one of three 12-week treatments: thrice-weekly sessions of yoga, aerobics or strength training; Internet-based cognitive-behavioral therapy; or standard counseling plus medication. Patients in all groups improved, but those engaging in exercise experienced the greatest benefits. Internet-based therapy came in as a close runner-up, but the typical treatment plan lagged behind both alternatives. To date, numerous meta-analyses have kept score on the accumulating data. They do not all agree: a few have found no indication that exercise is helpful or have found that it offers only very small effects or greatly diminished benefits in the long term. But most have reached similar optimistic conclusions. A 2013 review by the nonprofit organization Cochrane, regarded as a leader in evidence-based medicine, concluded that exercise is just as effective a treatment for depression as medication and counseling. A recent meta-analysis, published in 2016, echoes Cochrane’s finding. A team of international researchers examined 25 of the most rigorous experiments and determined that exercise, especially moderate to vigorous aerobic exercise under professional supervision, is indeed a potent treatment for depression. When they adjusted their analysis to account for weak studies—those most prone to some kind of experimental bias—they found an even stronger effect, suggesting that some previous meta-analyses may have underestimated exercise’s benefits for mental health. The researchers further calculated that it would take at least 1,000 contradictory studies to negate the affirming evidence that has piled up so far. Yet another review computed that when exercise is used to treat depression, success rates increase by as much as 67 to 74 percent. How Much Is Enough? Some researchers have attempted to figure out what types of exercise and intensity levels are most effective as

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an antidepressant. In a frequently cited study from 2005, for example, Trivedi and his colleagues tracked the health of 80 adults with mild to moderate depression for three months as they exercised three to five times a week on a treadmill or stationary bicycle at low intensity (seven kilocalories per kilogram per week) or at a higher intensity, as recommended by public health authorities (17.5 kilocalories per kilogram per week). At the end of the three months, the adults who exercised at the higher intensity had lessened the severity of their depression by 47 percent, compared with only 30 percent for the low-intensity group and 29 percent for a group who engaged in stretching rather than aerobic exercise. On the basis of studies such as this one, some psychologists, clinicians and health authorities have gone as far as publishing specific recommendations. Trivedi prescribes three to five 45- to 60-minute sessions of aerobic exercise (walking, running, cycling, or using a treadmill, stationary bike or elliptical trainer) each week at an intensity of 50 to 85 percent maximum heart rate. “The ideal is probably at least 16 kilocalories per kilogram of body weight, which works out to 1,200 to 1,500 kilocalories each week for average body weight,” Trivedi says. “If you can talk to your spouse on the phone, you’re not working out at the right intensity.” Likewise Central Queensland University exercise psychologist Robert Stanton advises 30- to 40-minute sessions of aerobic exercise—walking, cross training or stationary cycling—three to four times a week at low to moderate intensity for at least nine weeks. And the National Institute for Health and Care Excellence advocates group-based physical activity programs for patients with mild to moderate depression, consisting of at least three 45-minute sessions a week for at least 10 weeks. Other experts, however, think it may be too soon to get so specific. A 2013 review paper, for instance, concluded that both cardiovascular and resistance exercise, either alone or in combination, are effective at treating depression but that there are not yet enough data to definitively favor one form of physical activity over another. “Which exercise has the best mood effects, and what intensity is best? Does it work better alone or combined with other treatments? We don’t know for certain yet,” says psychologist Michael Otto of Boston University, who has studied both the emotional and cognitive benefits of exercise. “We can make some general suggestions, but we still need more data to be confident about the specifics.” Why Exercise Works In the past decade scientists have uncovered numerous details about how exercise alters the brain, and the body as a whole, in ways that alleviate and protect against depression. The second you start running, pedaling or lifting a dumbbell, your body’s chemistry begins to change. Exercise boosts your heart rate, sending blood, oxygen, hormones and neurochemicals surging through the body. In the moment, the body responds to exercise as a kind of stress—but it is ultimately beneficial. Some evidence suggests that habitual moderate exercise rewires the brain and immune system to better cope with physical and mental strain. The better the body becomes at dealing with stressors of all kinds, the lower the risk of a depressive episode. In fact, many researchers think of depression as a disorder of managing stress. Exercise also seems to mimic some of the chemical effects of antidepressant medication. Based on increasing evidence, some scientists argue that certain cases of depression result from the impaired growth of both brain cells and the connections between them. Studies have documented the atrophy and loss of neurons in brain regions such as the amygdala, hippocampus and prefrontal cortex in patients with major depression. Antidepressants that increase levels of serotonin and other neurotransmitters might work by reinvigorating neural proliferation, a process that depends in part on a molecule called brain-derived neurotrophic factor (BDNF). In studies with both animals and people, exercise enhances the production of BDNF. In one 2001 study, for example, rats given an antidepressant and the opportunity to run produced higher levels of BDNF compared with animals that only ran or only received medication. Moreover, they were better at enduring a stressful experience, swimming for longer in an inescapable water tank before giving up—a test designed to approximate the onset of depression. In an analogous human study in 2016, Brazilian researchers divided 57 adults taking the antidepressant sertraline for moderate to severe depression into two groups: one attended four weekly sessions of aerobic activity for 28 days, and the other did not exercise. Symptoms abated similarly in both groups, but the exercise group improved on lower doses of antidepressants. The authors suspect that exercise enhanced the biochemical effects of the drugs. Similar studies have shown that simply recommending healthy lifestyle changes,

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such as establishing better sleep routines and getting more exercise, can dramatically boost the efficacy of antidepressants from a mere 10 percent remission rate with the drugs alone to a 60 percent remission rate. And in a small but intriguing 2015 study, physician Helmuth Haslacher and his colleagues at the Medical University of Vienna in Austria compared the mental health and genomes of 55 elderly marathon runners and endurance bicyclists with those of 58 nonathletes. Among the nonathletes, they found a statistically significant correlation between the number of depressive symptoms these individuals experienced and a particular gene variant that interferes with normal BDNF production. Among the athletes, however, there was no such correlation. The researchers concluded that by stimulating BDNF production, long-term, vigorous aerobic exercise might actually counteract a genetic susceptibility to depression. Neurobiology may also explain why, in addition to exercise countering depression, the inverse seems to be true: correlations in epidemiological surveys suggest that physical inactivity, while sometimes the result of depression, may also be a major risk factor for subsequently developing it. In a 2014 study of more than 6,000 elderly U.K. citizens, the more time they spent watching television, the more likely they were to report symptoms of depression (although this was not true for other sedentary activities such as reading). Those who participated in some form of vigorous physical activity at least once a week experienced less depression. Likewise, a 2015 survey of nearly 5,000 Chinese college students found that the more time a student spent in front of a TV or computer screen, the more likely he or she was to have depressive symptoms. In contrast, the risk for depression dropped the more physically active a student was, regardless of age, gender or residential background. A meta-analysis of 24 studies, involving nearly 200,000 participants, reached the same conclusion: sedentary behavior was associated with an increased risk of depression. On average, active people are 45 percent less likely to be depressed than inactive people, according to the U.S. Office of Disease Prevention and Health Promotion. The Feel-Good Factor Beyond these physiological reasons, many social and psychological factors help to explain why working out can alleviate symptoms of depression. In comprehensive interviews, people who have struggled with the disorder say that exercise energizes them, gives them a sense of purpose and achievement, elevates their self-esteem and mood, regulates appetite and sleep cycles, and distracts them from negative thoughts. For those who exercise in a group, it can also provide a welcome opportunity for social interaction. First, though, many people with depression must overcome a severe lack of motivation. “We need to educate people and give them tools to help monitor their progress,” Trivedi says. “We make patients log in and communicate with us. If we find out they have skipped a day, we work with them to solve the problem and make sure that by the end of week, they complete their regimen.” Jennifer Carter, director of sport psychology at the Ohio State University Wexner Medical Center, has come up with a bevy of practical tips, among them: “Notice the facts,” she advises. “For example, there are 1,440 minutes in a day. Perhaps you can find 30 of those to exercise.” Getting over that initial hurdle of low motivation seems to depend in particular on how much satisfaction and self-agency people experience while working out. “Enjoyment is fundamentally linked to how much people stick with exercise,” Otto says. “I want them to do what is most fun and entertaining, whatever that might be.” Research suggests that exercise as therapy succeeds when people choose the type and intensity. Most people prefer a moderate intensity, around or just below the ventilatory threshold—the point at which breathing becomes noticeably labored. In 2011 Patrick Callaghan, head of health sciences at the University of Nottingham in England, and his colleagues asked 38 women with depression to exercise on treadmills in small groups three times a week, either at a prescribed intensity or one they personally selected. After a month, the women who chose how much to exert themselves had lower levels of depression and higher self-esteem compared with the other group. Despite the mounting evidence that exercise can remedy some forms of depression, skepticism persists in academia and health care, Trivedi notes. “There is this general bias that exercise is not a bona fide treatment—it’s just something you should do in addition to treatment, like trying to sleep and eat well,” he says. “Even though recognition of exercise as a treatment is increasing,” only some health insurance companies pay for gym time, he explains, and when they do, they often offer small temporary discounts. “I can prescribe a drug that costs $200 and insurance will pay, but they won’t give $40 to open a gym membership.”

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Patients will need to change their thinking as well. “It can be hard for patients to think of exercise as a form of treatment,” Otto comments. “We usually exercise to look good at the beach, to lose weight.” Most individuals do not understand the degree to which exercise can reshape their mood, too. “Even if you feel like pulling in and doing nothing, exercise pushes you out,” he adds. “Depression makes you feel like everything you’re about to do is useless and pointless. That’s exactly what exercise fights—you have to get up and go.” Looking for Motivation? Remember These Tips 10 minutes of exercise is better than none. Set yourself challenging but realistic goals. If you aren’t exercising at all, start by taking the stairs instead of the elevator or call a friend to schedule a walk once or twice a week. Identify what motivates you: if you are competitive, join a recreational sports league; if you are a social butterfly, join an exercise class; if you are a nature buff, go on a hike.

--Originally published: Scientific American MIND 28(1); 26-31 (January/February 2017).

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Take 2 Hikes and Call Me in the Morning by Nathaniel P. Morris A growing trend in medicine has doctors prescribing visits to parks for their patients. A pediatrician named Robert Zarr at Unity Health Care in Washington, D.C., has worked with the National Park Service and other institutions to create DC Park Rx, an initiative that helps health care providers prescribe activity in outdoor spaces to patients. And National Geographic recently highlighted the rise of this practice in Vermont, where doctors are now prescribing thousands of visits to state parks. In the last several years park prescription programs have spread nationwide, from Maine to California, South Dakota to New Mexico. Proponents of these programs promote outdoor activity as a means of tackling chronic medical conditions like obesity, high blood pressure and type 2 diabetes. But park prescriptions also hold considerable promise for patients suffering from mental health issues. A large body of evidence suggests that exposure to nature may promote mental well-being. A 2010 metaanalysis of 10 studies including over 1,200 participants found people who exercised in green environments demonstrated significant improvements in mood and self-esteem. A 2011 systematic review looked at 11 trials that compared indoor and outdoor activity, finding that exercise in natural settings was “associated with greater feelings of revitalization and positive engagement, decreases in tension, confusion, anger and depression, and increased energy.” Another recent review of studies found activity in natural environments correlated with reductions in negative emotions like sadness, anger and fatigue. Some studies suggest interactions with parks and other natural settings may influence rates of mental illness in the population. For example, a study of over 160,000 people in South Korea found those living in areas with the lowest amount of parks and green spaces had 20 percent greater odds of depressive symptoms and 28 percent greater odds of suicide attempts compared with those living in areas with the highest amount of natural spaces, even after controlling for potential confounders like age, gender and monthly income. Researchers are trying to better understand the neuroscience behind why exposure to parks and other natural settings might promote mental health. A study out of Stanford University, where I’m training as a resident physician in psychiatry, used brain imaging to examine participants who walked in urban or natural environments; the authors found those who went on a nature walk reported decreased rumination (that is, repetitive thoughts focused on negative aspects of the self) and had lower activity in the subgenual prefrontal cortex, a region of the brain associated with mental illness. These effects were not seen after urban walks. Given these promising results, it’s not surprising to see burgeoning interest in park prescription programs and other mental health treatments designed around exposure to nature. Researchers are exploring whether outdoor activities like hiking or horticulture may help treat veterans suffering from post-traumatic stress disorder. Multiple studies suggest outdoor exercise may be helpful in treating depression. Nature-assisted treatments have been associated with improved outcomes for conditions like schizophrenia as well as decreased levels of health care consumption among people with mental health issues. How park prescriptions work may vary depending on the health care provider and the patient’s location. In the model developed by DC Park Rx, clinicians can generate a prescription from a database that maps out local parks for patients with recommended activities and park ratings. A number of prescription programs rolled out by states now also waive park entrance fees for patients.

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But park prescriptions aren’t panaceas just yet. Many patients, including those who are working multiple jobs, unemployed or homeless, may not be able to travel or to take the time to enjoy the benefits of activity in nearby parks. And although park prescriptions are popping up across the country, we still have little data to confirm whether these programs have a meaningful impact on patients’ health—mental health or otherwise. Another concern raised by National Geographic’s coverage of park prescriptions is the potential misuse of these budding programs. In the article the chair of the Vermont Governor’s Council on Physical Fitness and Sports chastised some doctors for writing park prescriptions for their staffs instead of their patients. Another doctor at the University of Vermont Medical Center talked about how park prescriptions frequently end up stuffed into patients’ discharge paperwork without much discussion of what they’re for. As a doctor specializing in mental health, I still see a lot of good that can come from these programs. Parks are all around us, and a fair amount of evidence suggests they can help patients suffering from mental health issues. And as Zarr of DC Park Rx has pointed out, visiting a park has fewer side effects and lower costs compared with some of the medications we give our patients. During my residency training, I often see patients lying on stretchers in emergency department hallways, struggling to sleep in noisy intensive care units or sitting in windowless clinic rooms. Indeed, I wonder whether these environments say something about the kinds of treatment that we provide. Last month, I slipped away from the hospital during a weekend to do some hiking in a local park. As I walked along a ridge, the sounds of my pager faded from my consciousness. I listened to the trees as the sun warmed my face. A sense of calm came over me. That felt like good medicine. --Originally published: Scientific American Online, September 2017

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Índice Copyright Title Page Table of Contents Introduction SECTION 1 Breaking Biology: New Truths in Diet & Exercise 1.1 The Exercise Paradox 1.2 The Messy Truth about Weight Loss 1.3 The “True” Human Diet 1.4 Mind over Meal: Weight-Loss Surgery and the Gut-Brain Connection SECTION 2 The Skinny on Behavioral Intervention 2.1 Don’t Diet! 2.2 Behavior: The Additional Key to Weight-Loss SECTION 3 Mental Floss: Your Brain on Exercise 3.1 Head Strong 3.2 Take 2 Hikes and Call Me in the Morning

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