Monday, August 10, 2009

Why Exercise Won't Make You Thin - By John Cloud

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 Bulletin published 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."

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?

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."

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.


Related article: “What if It's All Been a Big Fat Lie?” By Gary Taubes

Related book: Good Calories, Bad Calories: Fats, Carbs, and the Controversial Science of Diet and Health

*Note: Nassim Taleb liked and reviewed this book HERE.


For more on exercise and the brain, see: Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School