Childhood obestity: Why existing efforts to combat it are bound to fail.

March 16 2011 10:20 PM

It's Not About the Calories

Why existing efforts to combat childhood obesity are bound to fail.

Read about Slate's project to generate new ideas for fighting childhood obesity here.      

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It's the carbs that hurt us

The past few years have seen the launch of many admirable initiatives to solve the problem of childhood obesity in America, but I'd like to respectfully suggest that these programs are, quite simply, doomed to failure. This is not because the food industry will subvert their efforts. It's not because the children and parents in this country lack the willpower to tackle this problem and certainly not because they lack the motivation. It's because the advice these anti-obesity initiatives give isn't going to help, and the science they're based on is misguided. 

Take Michelle Obama's Let's Move! campaign, one of the most high-profile examples of this mistaken approach to the problem. The principles of Let's Move! sound good. Who would be against getting kids to be more physically active and eat more fruits and vegetables? But anyone who thinks that will reverse the obesity epidemic is sorely mistaken.

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Beneath all the program's talk of making healthier food choices and increasing physical activity, its fundamental tenet is that we get fat because of the "overconsumption of calories." This is how the White House's Task Force on Childhood Obesity phrased the problem in its May 2010 report (PDF). And so the way to induce our children to lose weight is to get them to consume fewer calories, which they'll do supposedly by eating less-energy-dense foods, and, of course, expending more energy through exercise—hence the name, "Let's Move!"

This approach is certainly convenient. As Michelle Obama has said, it doesn't require the "demonization of any industry." All foods are OK in moderation, and the more our kids exercise, the more they can consume without getting fat. Follow this simple prescription and all will be well.

Except it won't be. For the last 60 years, physicians and public-health authorities have been giving that exact same advice to obese people—children and adults—with little or no success. When researchers have tested diets that restrict how many calories are consumed—counseling their subjects to eat, say, 500 or 1,000 fewer calories a day than they normally would—the results have been depressingly predictable. The subjects experience modest weight loss (maybe nine or 10 pounds in the first six months), and then they gain the weight right back. Weight loss doesn't last.

A conspicuous example of how these kinds of diets fail is the Women's Health Initiative, the largest and most expensive nutrition trial ever conducted. The researchers enrolled nearly 50,000 mostly overweight or obese women into the trial, chose roughly 20,000 of them at random, and instructed that group to eat a low-fat diet, rich in fruits, vegetables, and fiber. These women were given regular counseling to motivate them to stay on the diet. If we believe what these women said they were eating, they also cut their average energy intake by well more than 300 calories a day.

The result? After seven-plus years on the diet, these women lost an average of one pound each (PDF). And their average waist circumference—a measure of what the diet-book authors like to call "belly fat"—increased. This suggests that whatever weight these women lost was not fat but lean tissue—muscle. It also suggests that getting people to increase their consumption of fruits, vegetables, and whole grains is not the way to induce weight loss.

OK, so what about getting them to move more? Surprisingly, exercise is a relatively recent addition to the standard prescriptions for weight loss. Prior to the 1960s, clinicians used to argue that making an obese person exercise would just make them hungry—they'd work up an appetite—and that's the last thing you want for someone who needs to lose weight. Sure, healthy kids (and adults) are physically active, and lean kids (and adults) are more physically active than fat ones. But it doesn't mean you can turn obese kids (or adults) into lean ones just by putting them on a treadmill. Still, the idea that exercise could lead to weight loss took hold back in the 1970s—thanks in large part to the efforts of one influential nutritionist, Jean Mayer of Harvard University—and we've been hearing it ever since. By 1980, as the Washington Post reported at the time, about 100 million Americans had become active members of the "new fitness revolution … one of the late twentieth century's major sociological events."

The fact that this fitness revolution happened to coincide with the beginning of the present obesity epidemic is mostly a coincidence, but it certainly speaks to the idea that getting kids to move more is not the answer. Indeed, reviews of the efficacy of physical activity to induce any significant weight loss long-term are virtually unanimous that it doesn't.  The American Heart Association and the American College of Sports Medicine pointed out this fact back in 2007, when they published joint physical-activity guidelines (PDF). As they put it, the data supporting the idea that increasing our energy expenditure will lead to weight loss—or even a slowing of weight gain—"are not particularly compelling." Making it possible for children to enjoy the benefits of physical activity is a wonderful thing, but expecting that they'll lose weight by doing so is naive.