Rethinking Thin: The New Science of Weight Loss – and the Myths and Realities of Dieting, by Gina Kolata ( Farrar, Straus, and Giroux, 2007)

No one wants to be fat. Not only does American culture worship thinness, but overweight people earn less and marry less often than thinner people. Why, then, do so many otherwise smart people find it so difficult to lose weight?

This is the question at the heart of New York Times science writer Gina Kolata’s new book, Rethinking Thin. The book surveys the history and science of weight loss as it follows four dieters, who were part of a 360-person study comparing the low-carbohydrate Atkins diet with a more traditional calorie counting plan. The dieters struggle mightily to eat less and exercise more over the two year study. All lose about ten percent of their body weight in the first few months. But all of them gain the pounds back.

Maybe, she muses, there isn’t 'such a thing as free will when it comes to eating and body weight.'

With these earnest dieters’ stories as the backdrop, Kolata advances an intriguing thesis. What if it isn’t really possible for the average person to lose large amounts of weight, long term? What if our bodies have a set point that every cell struggles mightily to maintain? Maybe, she muses, there isn’t “such a thing as free will when it comes to eating and body weight.”

She has serious science to back this up. Researchers have found that the bodies of formerly fat people and naturally thin people are not alike, even when they weigh the same. The formerly fat will require far fewer calories to maintain their weight. While naturally thin people can fatten themselves up briefly (as a few actresses have done for parts), they lose the weight effortlessly afterwards. Naturally fat people’s bodies, on the other hand, want to stay fat. To become and stay thin, a formerly fat person has to eat far fewer calories than his naturally thin counterpart—fewer than he’d like, and fewer than will be comfortable. One famous World War II-era study of conscientious objectors restricted to half their normal food intake showed that they soon became obsessed. They dreamed of food. They developed elaborate rituals. Few people can live like this for long, no matter how disciplined they may be.

Of course, human metabolic dispositions have not changed as quickly as the fraction of Americans who are overweight or obese has. Kolata does not completely discount environmental factors. Her belief in a human “set point” for weight is not an absolute doctrine; as she writes, “The research shows that individuals have a range of weights, often spanning as much as 20 or 30 pounds, that they can achieve and sustain.” If we eat well and exercise, we’ll hover near the bottom of that range and feel better physically. If we hit the donuts too often, we’ll rise to the top. It’s when we attempt to cross that 30 lb boundary that our bodies rebel. But since longevity is rising even as two-thirds of Americans are overweight or obese, it may turn out that the obesity “crisis” is not as dire as public health nags make it out to be. Perhaps our thin ideals—Hollywood types with flawless figures—have always been as unrealistic as our faddish diets.

Rethinking Thin dances close to becoming just another litany of excuses in a field that features many.

It’s a fascinating argument. Unfortunately, Kolata undermines it by ignoring the small proportion of dieters who have managed to keep off massive amounts of weight for years. These people aren’t hard to find. The National Weight Control Registry (run partly by Prof. James O. Hill of the University of Colorado, whose other work Kolata cites) features 5,000 people who’ve lost more than 30 lbs and kept it off for more than a year. Many of these people have been profiled in other diet books, and are happy to talk about their experiences. Without an explanation for these dieters’ successes, Rethinking Thin dances close to becoming just another litany of excuses in a field that features many.

Still, fans of Kolata’s writing in the Times will not be disappointed by this book. She has an easy way of explaining complicated science, of introducing you to words like “leptin” and “ghrelin” without scaring you off. Rethinking Thin will definitely make you smarter about the world of metabolism and nutrition, even if you despair, after reading it, of ever looking like Brad Pitt.

Laura Vanderkam is the author of Grindhopping: Build a Rewarding Career without Paying Your Dues.