Doctors aren’t supposed to write prescriptions for medications they know don’t work. So why do they and many leading public health authorities continue to dispense advice that may be no more effective than a sugar pill—and might actually cause harm? In a landmark review published earlier this year in Nutrition Journal, the authors question why doctors and other medical experts routinely counsel over-weight people to get rid of extra pounds even though scientists, after decades of intense research, have yet to find a reliable prescription for weight loss. Moreover, the payoff for dieting isn’t even clear: There’s little evidence that losing weight is the key to better health, contends lead author Linda Bacon, PhD, a nutrition professor at the City College of San Francisco. And in some cases, she adds, efforts to shed pounds may actually be dangerous.

In her well-informed critique, Bacon not only raises questions about conventional weight-loss notions but also posits that there are more effective paths to better health. More asked her for details.

What’s wrong with dieting—that is, restricting your food intake to lose weight?
A The first thing that’s wrong is that dieting almost never works. A few years ago, psychologist Traci Mann, PhD, and her colleagues at the University of California, Los Angeles, reviewed two decades of studies of weight-loss programs. They found that dieters initially dropped pounds, usually 5 to 10 percent of their body weight. But when these dieters were followed over time, they almost all regained the weight they’d lost. In general, the more time that passes after someone loses weight on a diet, the more weight she regains, until she’s back to where she was or is even heavier. Results like these led a panel of experts convened by the National Institutes of Health to acknowledge that no matter what weight-loss plan people follow, almost all of them regain weight. There’s no evidence that diets lead to lasting weight loss.

But aren’t there some successful losers out there? Hasn’t the National Weight Control Registry [NWCR] been keeping a list of them in order to figure out what works?
A Of course there are successes. But very, very few. The NWCR tracks people who have lost 30 pounds or more, but for as little as one year. Also, the number of people in the registry is a tiny portion of the total group of Americans trying to lose weight. In general, the scientific and popular literature estimates that only about 5 percent of dieters maintain their weight loss, which is dismal. To insist that everyone do what only a small fraction of people have succeeded at is to set up the majority for failure. It’s not that dieters fail. It’s the concept of dieting that fails.

Still, Americans have grown fatter over the past 30 years. Don’t we need to stem the rising epidemic of obesity?
A The term epidemic is misleading. It’s true that average weight has increased. But the word epidemic implies a public health crisis. There’s no evidence that Americans’ being heavier, on average, poses a serious health threat.