Sunday, Aug. 09, 2009
Why Exercise Won't Make You Thin
By John Cloud
As I write this, tomorrow is Tuesday, which is a cardio day. I'll spend five minutes warming up on the VersaClimber, a towering machine that requires you to move your arms and legs simultaneously. Then I'll do 30 minutes on a stair mill. On Wednesday a personal trainer will work me like a farm animal for an hour, sometimes to the point that I am dizzy — an abuse for which I pay as much as I spend on groceries in a week. Thursday is "body wedge" class, which involves another exercise contraption, this one a large foam wedge from which I will push myself up in various hateful ways for an hour. Friday will bring a 5.5-mile run, the extra half-mile my grueling expiation of any gastronomical indulgences during the week.
I have exercised like this — obsessively, a bit grimly — for years, but recently I began to wonder: Why am I doing this? Except for a two-year period at the end of an unhappy relationship — a period when I self-medicated with lots of Italian desserts — I have never been overweight. One of the most widely accepted, commonly repeated assumptions in our culture is that if you exercise, you will lose weight. But I exercise all the time, and since I ended that relationship and cut most of those desserts, my weight has returned to the same 163 lb. it has been most of my adult life. I still have gut fat that hangs over my belt when I sit. Why isn't all the exercise wiping it out? (Read "The Year in Medicine 2008: From A to Z.")
It's a question many of us could ask. More than 45 million Americans now belong to a health club, up from 23 million in 1993. We spend some $19 billion a year on gym memberships. Of course, some people join and never go. Still, as one major study — the Minnesota Heart Survey — found, more of us at least say we exercise regularly. The survey ran from 1980, when only 47% of respondents said they engaged in regular exercise, to 2000, when the figure had grown to 57%.
And yet obesity figures have risen dramatically in the same period: a third of Americans are obese, and another third count as overweight by the Federal Government's definition. Yes, it's entirely possible that those of us who regularly go to the gym would weigh even more if we exercised less. But like many other people, I get hungry after I exercise, so I often eat more on the days I work out than on the days I don't. Could exercise actually be keeping me from losing weight? (Watch TIME's video "How to Lose Hundreds of Pounds.")
The conventional wisdom that exercise is essential for shedding pounds is actually fairly new. As recently as the 1960s, doctors routinely advised against rigorous exercise, particularly for older adults who could injure themselves. Today doctors encourage even their oldest patients to exercise, which is sound advice for many reasons: People who regularly exercise are at significantly lower risk for all manner of diseases — those of the heart in particular. They less often develop cancer, diabetes and many other illnesses. But the past few years of obesity research show that the role of exercise in weight loss has been wildly overstated. (Read "Losing Weight: Can Exercise Trump Genes?")
"In general, for weight loss, exercise is pretty useless," says Eric Ravussin, chair in diabetes and metabolism at Louisiana State University and a prominent exercise researcher. Many recent studies have found that exercise isn't as important in helping people lose weight as you hear so regularly in gym advertisements or on shows like The Biggest Loser — or, for that matter, from magazines like this one.
The basic problem is that while it's true that exercise burns calories and that you must burn calories to lose weight, exercise has another effect: it can stimulate hunger. That causes us to eat more, which in turn can negate the weight-loss benefits we just accrued. Exercise, in other words, isn't necessarily helping us lose weight. It may even be making it harder.
The Compensation Problem
Earlier this year, the peer-reviewed journal PLoS ONE — PLoS is the nonprofit Public Library of Science — published a remarkable study supervised by a colleague of Ravussin's, Dr. Timothy Church, who holds the rather grand title of chair in health wisdom at LSU. Church's team randomly assigned into four groups 464 overweight women who didn't regularly exercise. Women in three of the groups were asked to work out with a personal trainer for 72 min., 136 min., and 194 min. per week, respectively, for six months. Women in the fourth cluster, the control group, were told to maintain their usual physical-activity routines. All the women were asked not to change their dietary habits and to fill out monthly medical-symptom questionnaires.
Earlier this year, the peer-reviewed journal PLoS ONE — PLoS is the nonprofit Public Library of Science — published a remarkable study supervised by a colleague of Ravussin's, Dr. Timothy Church, who holds the rather grand title of chair in health wisdom at LSU. Church's team randomly assigned into four groups 464 overweight women who didn't regularly exercise. Women in three of the groups were asked to work out with a personal trainer for 72 min., 136 min., and 194 min. per week, respectively, for six months. Women in the fourth cluster, the control group, were told to maintain their usual physical-activity routines. All the women were asked not to change their dietary habits and to fill out monthly medical-symptom questionnaires.
The findings were surprising. On average, the women in all the groups, even the control group, lost weight, but the women who exercised — sweating it out with a trainer several days a week for six months — did not lose significantly more weight than the control subjects did. (The control-group women may have lost weight because they were filling out those regular health forms, which may have prompted them to consume fewer doughnuts.) Some of the women in each of the four groups actually gained weight, some more than 10 lb. each.
What's going on here? Church calls it compensation, but you and I might know it as the lip-licking anticipation of perfectly salted, golden-brown French fries after a hard trip to the gym. Whether because exercise made them hungry or because they wanted to reward themselves (or both), most of the women who exercised ate more than they did before they started the experiment. Or they compensated in another way, by moving around a lot less than usual after they got home. (Read "Run For Your Lives.")
The findings are important because the government and various medical organizations routinely prescribe more and more exercise for those who want to lose weight. In 2007 the American College of Sports Medicine and the American Heart Association issued new guidelines stating that "to lose weight ... 60 to 90 minutes of physical activity may be necessary." That's 60 to 90 minutes on most days of the week, a level that not only is unrealistic for those of us trying to keep or find a job but also could easily produce, on the basis of Church's data, ravenous compensatory eating.
It's true that after six months of working out, most of the exercisers in Church's study were able to trim their waistlines slightly — by about an inch. Even so, they lost no more overall body fat than the control group did. Why not?
Church, who is 41 and has lived in Baton Rouge for nearly three years, has a theory. "I see this anecdotally amongst, like, my wife's friends," he says. "They're like, 'Ah, I'm running an hour a day, and I'm not losing any weight.'" He asks them, "What are you doing after you run?" It turns out one group of friends was stopping at Starbucks for muffins afterward. Says Church: "I don't think most people would appreciate that, wow, you only burned 200 or 300 calories, which you're going to neutralize with just half that muffin." (Read "Too Fat? Read Your E-mail.")
You might think half a muffin over an entire day wouldn't matter much, particularly if you exercise regularly. After all, doesn't exercise turn fat to muscle, and doesn't muscle process excess calories more efficiently than fat does?
Yes, although the muscle-fat relationship is often misunderstood. According to calculations published in the journal Obesity Research by a Columbia University team in 2001, a pound of muscle burns approximately six calories a day in a resting body, compared with the two calories that a pound of fat burns. Which means that after you work out hard enough to convert, say, 10 lb. of fat to muscle — a major achievement — you would be able to eat only an extra 40 calories per day, about the amount in a teaspoon of butter, before beginning to gain weight. Good luck with that.
Fundamentally, humans are not a species that evolved to dispose of many extra calories beyond what we need to live. Rats, among other species, have a far greater capacity to cope with excess calories than we do because they have more of a dark-colored tissue called brown fat. Brown fat helps produce a protein that switches off little cellular units called mitochondria, which are the cells' power plants: they help turn nutrients into energy. When they're switched off, animals don't get an energy boost. Instead, the animals literally get warmer. And as their temperature rises, calories burn effortlessly. (See TIME's health and medicine covers.)
Because rodents have a lot of brown fat, it's very difficult to make them obese, even when you force-feed them in labs. But humans — we're pathetic. We have so little brown fat that researchers didn't even report its existence in adults until earlier this year. That's one reason humans can gain weight with just an extra half-muffin a day: we almost instantly store most of the calories we don't need in our regular ("white") fat cells.
All this helps explain why our herculean exercise over the past 30 years — all the personal trainers, StairMasters and VersaClimbers; all the Pilates classes and yoga retreats and fat camps — hasn't made us thinner. After we exercise, we often crave sugary calories like those in muffins or in "sports" drinks like Gatorade. A standard 20-oz. bottle of Gatorade contains 130 calories. If you're hot and thirsty after a 20-minute run in summer heat, it's easy to guzzle that bottle in 20 seconds, in which case the caloric expenditure and the caloric intake are probably a wash. From a weight-loss perspective, you would have been better off sitting on the sofa knitting.
Self-Control Is like a Muscle
Many people assume that weight is mostly a matter of willpower — that we can learn both to exercise and to avoid muffins and Gatorade. A few of us can, but evolution did not build us to do this for very long. In 2000 the journal Psychological Bulletinpublished a paper by psychologists Mark Muraven and Roy Baumeister in which they observed that self-control is like a muscle: it weakens each day after you use it. If you force yourself to jog for an hour, your self-regulatory capacity is proportionately enfeebled. Rather than lunching on a salad, you'll be more likely to opt for pizza.
Many people assume that weight is mostly a matter of willpower — that we can learn both to exercise and to avoid muffins and Gatorade. A few of us can, but evolution did not build us to do this for very long. In 2000 the journal Psychological Bulletinpublished a paper by psychologists Mark Muraven and Roy Baumeister in which they observed that self-control is like a muscle: it weakens each day after you use it. If you force yourself to jog for an hour, your self-regulatory capacity is proportionately enfeebled. Rather than lunching on a salad, you'll be more likely to opt for pizza.
Some of us can will ourselves to overcome our basic psychology, but most of us won't be very successful. "The most powerful determinant of your dietary intake is your energy expenditure," says Steven Gortmaker, who heads Harvard's Prevention Research Center on Nutrition and Physical Activity. "If you're more physically active, you're going to get hungry and eat more." Gortmaker, who has studied childhood obesity, is even suspicious of the playgrounds at fast-food restaurants. "Why would they build those?" he asks. "I know it sounds kind of like conspiracy theory, but you have to think, if a kid plays five minutes and burns 50 calories, he might then go inside and consume 500 calories or even 1,000." (Read "Why Kids' Exercise Matters Less Than We Think.")
Last year the International Journal of Obesity published a paper by Gortmaker and Kendrin Sonneville of Children's Hospital Boston noting that "there is a widespread assumption that increasing activity will result in a net reduction in any energy gap" — energy gap being the term scientists use for the difference between the number of calories you use and the number you consume. But Gortmaker and Sonneville found in their 18-month study of 538 students that when kids start to exercise, they end up eating more — not just a little more, but an average of 100 calories more than they had just burned.
If evolution didn't program us to lose weight through exercise, what did it program us to do? Doesn't exercise do anything?
Sure. It does plenty. In addition to enhancing heart health and helping prevent disease, exercise improves your mental health and cognitive ability. A study published in June in the journal Neurology found that older people who exercise at least once a week are 30% more likely to maintain cognitive function than those who exercise less. Another study, released by the University of Alberta a few weeks ago, found that people with chronic back pain who exercise four days a week have 36% less disability than those who exercise only two or three days a week.
But there's some confusion about whether it is exercise — sweaty, exhausting, hunger-producing bursts of activity done exclusively to benefit our health — that leads to all these benefits or something far simpler: regularly moving during our waking hours. We all need to move more — the Centers for Disease Control and Prevention says our leisure-time physical activity (including things like golfing, gardening and walking) has decreased since the late 1980s, right around the time the gym boom really exploded. But do we need to stress our bodies at the gym?
Look at kids. In May a team of researchers at Peninsula Medical School in the U.K. traveled to Amsterdam to present some surprising findings to the European Congress on Obesity. The Peninsula scientists had studied 206 kids, ages 7 to 11, at three schools in and around Plymouth, a city of 250,000 on the southern coast of England. Kids at the first school, an expensive private academy, got an average of 9.2 hours per week of scheduled, usually rigorous physical education. Kids at the two other schools — one in a village near Plymouth and the other an urban school — got just 2.4 hours and 1.7 hours of PE per week, respectively.
To understand just how much physical activity the kids were getting, the Peninsula team had them wear ActiGraphs, light but sophisticated devices that measure not only the amount of physical movement the body engages in but also its intensity. During four one-week periods over consecutive school terms, the kids wore the ActiGraphs nearly every waking moment.
And no matter how much PE they got during school hours, when you look at the whole day, the kids from the three schools moved the same amount, at about the same intensity. The kids at the fancy private school underwent significantly more physical activity before 3 p.m., but overall they didn't move more. "Once they get home, if they are very active in school, they are probably staying still a bit more because they've already expended so much energy," says Alissa Frémeaux, a biostatistician who helped conduct the study. "The others are more likely to grab a bike and run around after school."
Another British study, this one from the University of Exeter, found that kids who regularly move in short bursts — running to catch a ball, racing up and down stairs to collect toys — are just as healthy as kids who participate in sports that require vigorous, sustained exercise.
Could pushing people to exercise more actually be contributing to our obesity problem? In some respects, yes. Because exercise depletes not just the body's muscles but the brain's self-control "muscle" as well, many of us will feel greater entitlement to eat a bag of chips during that lazy time after we get back from the gym. This explains why exercise could make you heavier — or at least why even my wretched four hours of exercise a week aren't eliminating all my fat. It's likely that I am more sedentary during my nonexercise hours than I would be if I didn't exercise with such Puritan fury. If I exercised less, I might feel like walking more instead of hopping into a cab; I might have enough energy to shop for food, cook and then clean instead of ordering a satisfyingly greasy burrito.
Closing the Energy Gap
The problem ultimately is about not exercise itself but the way we've come to define it. Many obesity researchers now believe that very frequent, low-level physical activity — the kind humans did for tens of thousands of years before the leaf blower was invented — may actually work better for us than the occasional bouts of exercise you get as a gym rat. "You cannot sit still all day long and then have 30 minutes of exercise without producing stress on the muscles," says Hans-Rudolf Berthoud, a neurobiologist at LSU's Pennington Biomedical Research Center who has studied nutrition for 20 years. "The muscles will ache, and you may not want to move after. But to burn calories, the muscle movements don't have to be extreme. It would be better to distribute the movements throughout the day."
The problem ultimately is about not exercise itself but the way we've come to define it. Many obesity researchers now believe that very frequent, low-level physical activity — the kind humans did for tens of thousands of years before the leaf blower was invented — may actually work better for us than the occasional bouts of exercise you get as a gym rat. "You cannot sit still all day long and then have 30 minutes of exercise without producing stress on the muscles," says Hans-Rudolf Berthoud, a neurobiologist at LSU's Pennington Biomedical Research Center who has studied nutrition for 20 years. "The muscles will ache, and you may not want to move after. But to burn calories, the muscle movements don't have to be extreme. It would be better to distribute the movements throughout the day."
For his part, Berthoud rises at 5 a.m. to walk around his neighborhood several times. He also takes the stairs when possible. "Even if people can get out of their offices, out from in front of their computers, they go someplace like the mall and then take the elevator," he says. "This is the real problem, not that we don't go to the gym enough." (Read "Is There a Laziness Gene?")
I was skeptical when Berthoud said this. Don't you need to raise your heart rate and sweat in order to strengthen your cardiovascular system? Don't you need to push your muscles to the max in order to build them?
Actually, it's not clear that vigorous exercise like running carries more benefits than a moderately strenuous activity like walking while carrying groceries. You regularly hear about the benefits of exercise in news stories, but if you read the academic papers on which these stories are based, you frequently see that the research subjects who were studied didn't clobber themselves on the elliptical machine. A routine example: in June the Association for Psychological Science issued a news release saying that "physical exercise ... may indeed preserve or enhance various aspects of cognitive functioning." But in fact, those who had better cognitive function merely walked more and climbed more stairs. They didn't even walk faster; walking speed wasn't correlated with cognitive ability.
There's also growing evidence that when it comes to preventing certain diseases, losing weight may be more important than improving cardiovascular health. In June, Northwestern University researchers released the results of the longest observational study ever to investigate the relationship between aerobic fitness and the development of diabetes. The results? Being aerobically fit was far less important than having a normal body mass index in preventing the disease. And as we have seen, exercise often does little to help heavy people reach a normal weight. (Read "Physical Fitness — How Not to Get Sick.")
So why does the belief persist that exercise leads to weight loss, given all the scientific evidence to the contrary? Interestingly, until the 1970s, few obesity researchers promoted exercise as critical for weight reduction. As recently as 1992, when a stout Bill Clinton became famous for his jogging and McDonald's habits, the American Journal of Clinical Nutrition published an article that began, "Recently, the interest in the potential of adding exercise to the treatment of obesity has increased." The article went on to note that incorporating exercise training into obesity treatment had led to "inconsistent" results. "The increased energy expenditure obtained by training may be compensated by a decrease in non-training physical activities," the authors wrote.
Then how did the exercise-to-lose-weight mantra become so ingrained? Public-health officials have been reluctant to downplay exercise because those who are more physically active are, overall, healthier. Plus, it's hard even for experts to renounce the notion that exercise is essential for weight loss. For years, psychologist Kelly Brownell ran a lab at Yale that treated obese patients with the standard, drilled-into-your-head combination of more exercise and less food. "What we found was that the treatment of obesity was very frustrating," he says. Only about 5% of participants could keep the weight off, and although those 5% were more likely to exercise than those who got fat again, Brownell says if he were running the program today, "I would probably reorient toward food and away from exercise." In 2005, Brownell co-founded Yale's Rudd Center for Food Policy and Obesity, which focuses on food marketing and public policy — not on encouraging more exercise.
Some research has found that the obese already "exercise" more than most of the rest of us. In May, Dr. Arn Eliasson of the Walter Reed Army Medical Center reported the results of a small study that found that overweight people actually expend significantly more calories every day than people of normal weight — 3,064 vs. 2,080. He isn't the first researcher to reach this conclusion. As science writer Gary Taubes noted in his 2007 book Good Calories, Bad Calories: Fats, Carbs, and the Controversial Science of Diet and Health, "The obese tend to expend more energy than lean people of comparable height, sex, and bone structure, which means their metabolism is typically burning off more calories rather than less."
In short, it's what you eat, not how hard you try to work it off, that matters more in losing weight. You should exercise to improve your health, but be warned: fiery spurts of vigorous exercise could lead to weight gain. I love how exercise makes me feel, but tomorrow I might skip the VersaClimber — and skip the blueberry bar that is my usual postexercise reward.
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The latest health news is a surprise: “Exercise won’t make you thin.”
That Time magazine cover story appeared following a visit by one of its reporters to our campus. So, I feel compelled to offer a correction to a story that drifted off course to the conclusion that exercise is not useful for weight loss and weight management. Granted, exercise and its benefits can be a complex story. Even our own scientists discuss the relative importance of eating less or exercising more to lose weight and keep it off. To use a journalistic term, these findings would make interesting “sidebars” to a main story. However, to conclude that exercise is “useless” in the management of body weight is sending an unhealthy message. Most scientific evidence based on animal and human studies shows that regular exercise is a critical component of weight loss and weight control. Right now, only about five-percent of the U.S. adult population meets the current national recommendation of 30 minutes of moderate intensity exercise five days a week, when exercise level is objectively measured. So any story that discourages exercise is counterproductive. The Time article raised three issues to incorrectly conclude exercise won’t help you lose weight.
First issue - eating less is really the only way to lose weight. Yes, it is obviously easier to eat less than to exercise more. But many individuals have successfully lost weight simply by increasing exercise. It can be done. The physiology is real. Bodies stay at the same weight when a caloric balance is achieved. Under controlled laboratory conditions we see that when the amount of calories eaten equals calories used by activity and exercise, then weight remains the same. Participants lose weight when they use more calories than they eat and gain weight when they eat more calories than they use up. That means the body doesn’t care whether it loses calories by eating less or exercising more, the response is the same; weight is lost. So a diet in which you cut 300 calories a day will have more or less the same effect as activity that expends 300 extra calories a day. So, it may be easier to reduce your calories by eating less than by exercising more, but this does not mean exercise is “useless.” In fact, we gain many other health benefits by exercising, like lower blood pressure and a healthier heart and cardiovascular system.
Second issue - people succumb to so-called dietary compensation, meaning that after exercising, we get hungry and eat more, or “reward” ourselves with a snack. The fact is that millions of regularly active people tend to be normal weight. They may eat more, but it equals their level of energy expenditure. For instance, elite athletes in physically demanding sports may consume on a regular basis more than 5,000 calories per day and yet be quite lean and muscular. For the general public, we should base the main message on the preponderance of the evidence, which says that if you exercise regularly you will increase your caloric intake to meet the demand of your physically active lifestyle. I know of no credible evidence demonstrating that people overindulge in food just because they engaged in a bout of exercise. Such people can undoubtedly be found, but it is a small minority among those who engage in exercise. In the aggregate, we know of no study that concludes exercise causes enough overeating to increase body weight and reverse the health benefits. However, we do know that appetite is typically depressed after a bout of vigorous exercise. As a matter of fact, regular exercise is one of the most efficient ways to help keep caloric intake at the right level for you.
Final issue - those who exercise regularly may offset the effort by reducing their other daily activity and thus expend fewer calories than expected. This particular issue is complex as there are considerable individual differences in post exercise behavior. There are a few studies on both sides of this issue, but on balance more studies show that such compensation does not occur. Ironically just as the TIME issue came out, a group of researchers from Duke University published results showing daily exercise did not lead to a decrease in other activity for the remainder of the day.
Despite the confusion caused by the latest headline, we should rely on the vast majority of evidence that shows moderate activity or exercise should be part of any plan to lose weight, keep it off, and become healthier.
Claude Bouchard, Ph.D.
Executive Director
Pennington Biomedical Research Center
Baton Rouge, LA
By Cedric X. Bryant, Ph.D., F.A.C.S.M., Chief Science Officer, American Council on Exercise
Update: The researchers at Pennington Biomedical Research Center that were quoted in the Time article respond to the author’s inaccuracies in a follow-up statement.
The cover story of the August 9, 2009, issue of Time magazine featured an article entitled, “Why Exercise Won’t Make You Thin.” In this piece, author John Cloud made several inaccurate and unsubstantiated claims regarding the value of exercise, particularly as it relates to weight loss. What follows is a summary of some of the most misleading assertions made in this highly publicized article, as well as the American Council on Exercise’s response to these assertions:
- First and foremost, the article categorically implies that exercise has no meaningful role in weight loss. Such a conclusion is as false as it is reckless. The author’s “evidence” is the fact that he has “gut fat that hangs over his belt when he sits,” despite maintaining a regular exercise habit. In all likelihood, his unwanted abdominal girth is probably a by-product of genetics and/or consuming more calories than he expends.
- Weight loss and maintenance are a matter of simple accounting that is dependent upon energy balance. In order for weight loss to occur, individuals must burn more calories than they consume. Regrettably, many individuals who regularly exercise are unable to meet their weight-loss goals because they eat too much. In reality, however, their “personal weight situation” and overall health profile would be far worse were it not for the extra calories they expend while exercising.
- An overwhelming body of scientific evidence exists that confirms the positive role that exercise plays in weight loss and maintenance (Hill and Wyatt, 2005; Jakicic and Gallagher, 2003; Jakicic et al., 2001). These findings refute the notion (advanced by the author) that exercise impairs weight-loss efforts by substantially and uncontrollably increasing appetite. Recent research suggests that appetite may be suppressed for 60-90 minutes following vigorous exercise by affecting the release of certain appetite hormones. It also appears that aerobic exercise is more effective at suppressing appetite than non-aerobic forms of exercise (Broom et al., 2009). In general, individuals who participate in moderate exercise tend to eat approximately the same number of calories (or only slightly more) than they would if they did not exercise. Elite-level athletes typically consume high volumes of food after their exercise workouts, but they almost always expend more calories than they consumed (Blundell and King, 1999). It is important to keep in mind, however, that appetite is influenced several factors and is a very complex process making it difficult to generalize the impact of exercise on appetite. The bottom-line is that exercise and diet go hand-in-hand with successful weight management.
- Surprisingly (and disappointingly) the author failed to mention the tremendously important role that exercise plays in the maintenance of weight loss. According to data from the renowned National Weight Control Registry, consistent exercise participation is the single best predictor of long-term weight maintenance. In others words, if individuals want to be successful in getting off the weight-loss rollercoaster (i.e., repeatedly losing weight and regaining it), they need to regularly engage in physical activity.
- Another particularly bothersome portion of the article was the misleading comments regarding children and physical activity. A preponderance of evidence shows that kids are often less active after school, not more active as the article implies. As such, community-based youth fitness programs and high-quality school physical education programs are much needed. The available statistics support the fact that well-designed fitness programs aimed at encouraging children to be more active and maintain a healthy body weight remain a significant priority (HHS, 2008).
Needless to say, readers of this article in Time are likely to conclude that exercise is of little to no benefit to them, which makes its publication in such a high profile and respected magazine so disappointing—and possibly even dangerous. Given the enormous economic costs associated with obesity (approximately $147 billion annually), we should be promoting and advocating scientifically proven healthful behaviors like regular exercise participation whenever and wherever we can. Beyond its weight-control benefits, regular exercise provides a plethora of health benefits, including the treatment and prevention of a wide variety of chronic illnesses (heart disease, hypertension, diabetes, certain types of cancer, to name a few), an enhancement of psychological health and well-being, and an improvement in the overall quality of life throughout the human lifespan.
References
Blundell, J.E. & King, N.A. (1999). Physical activity and regulation of food intake: Current evidence. Medicine & Science in Sports & Exercise, 31, 11 Suppl., S573-S583.
Broom, D.R. et al. (2009). Influence of resistance and aerobic exercise on hunger, circulating levels of acylated ghrelin, peptide YY in healthy males.American Journal of Regulatory, Integrative and Comparative Physiology, 296, 1, R29-35.
Hill, J.O. and Wyatt, H.R. (2005). Role of physical activity in preventing and treating obesity. Journal of Applied Physiology, 99, 765-770.
Jakicic, J.M. & Gallagher, K.I. (2003). Exercise considerations for the sedentary, overweight adult. Exercise and Sport Sciences Reviews, 31, 2, 91-95.
Jakicic, J.M. et al. (2001). ACSM position stand on the appropriate intervention strategies for weight loss and prevention of weight regain for adults.Medicine & Science in Sports & Exercise, 33, 2145-2156.
U.S. Department of Health and Human Services (2008). 2008 Physical Activity Guidelines for Americans. Washington, D.C.: Department of Health and Human Services.
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