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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."
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."
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.
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.