It showed that adolescents who diet are more likely to engage in future binge eating. But this doesn't rule out the worrisome possibility that dieting also alters the body's metabolism so that calories later cling more tenaciously.
Does dieting have other health benefits? In the short-term, yes. Many brief trials have shown the benefit of diets for people at risk for type 2 diabetes and osteoarthritis, and for lowering high blood pressure. For the limited time that they reduced their caloric intake, patients with these conditions realized real gains.
The problem is that the benefits are erased by the typical return of those stubborn pounds. And as with the higher-than-ever weight gains, the aftereffects of dieting may cause additional basic health problems. Weight cycling—the common up-and-down yo-yoing of the scale—seems to have especially pernicious effects and is associated with higher blood pressure and heightened risk for heart attack, stroke, and diabetes.
What to make of all this? Mann's analysis casts serious doubt on the value of dieting for weight control. In my pediatric practice, I've become increasingly reluctant to push dieting on children, even very heavy ones. Though it's contrary to my own years-long cultivation of sloth, I am coming to believe ever more strongly in the value of pleasurable exercise for weight control and for independent health benefits, as demonstrated in innumerable medical studies. The problem, of course, is persuading the noninclined of the "pleasurable" part.
Ultimately, I think we need to start at the other end: by preventing kids from putting on excess weight in the first place. There's no easy fix, but in addition to increasing exercise, we need to somehow encourage families to shop and live differently. Perhaps we need to devise new kinds of calorie-limiting diets that don't make people feel deprived, because the hard fact is that they should never stop dieting. And, of course, we all hope for a magic pill to come out of the huge body of research now devoted to understanding how hormones regulate appetite and how the body's weight thermostat is controlled.
One other possibility. For a few people, dieting is effective. In one recent study, although more than 90 percent of the participants were no thinner after a year (and may gain more weight as time passes), about 7.5 percent continued to lose weight. Maybe we need to figure out just what contributed to these unusual success stories—and then find a way to apply it to the rest of us.