Of all the dangerous ideas that health officials could have embraced while trying to understand why we get fat, they would have been hard-pressed to find one ultimately more damaging than calories-in/calories-out. That it reinforces what appears to be so obvious - obesity as the penalty for gluttony and sloth - is what makes it so alluring. But it's misleading and misconceived on so many levels that it's hard to imagine how it survived unscathed and virtually unchallenged for the last fifty years. It has done incalculable harm. Not only is this thinking at least partly responsible for the ever-growing numbers of obese and overweight in the world - while directing attention away from the real reasons we get fat - but it has served to reinforce the perception that those who get fat have no one to blame but themselves. That eating less invariably fails as a cure for obesity is rarely perceived as the single most important reason to make us question our assumptions, as Hilde Bruch suggested half a century ago. Rather, it is taken as still more evidence that the overweight and obese are incapable of following a diet and eating in moderation. And it put the blame for their physical condition squarely on their behavior, which couldn't be further from the truth.