Eat less; exercise more. I’ve said it myself, in print (sorry about that, guys). This weight-loss advice isn’t wrong exactly, but it’s terribly incomplete. The causes of obesity are complex, and a sudden worldwide epidemic of people lacking willpower is definitely not the answer.
When people go on a diet, they usually lose weight. And then, with the same predictability, over the next few years the vast majority of dieters gain it back. Most of us blame ourselves, without appreciating the powerful biology that underlies the process. Substantial weight loss increases hunger and reduces metabolism – meaning that a successful dieter must eat less (forever) than someone of the same weight who’s always been thin.
The data on long-term outcomes of dieting that I presented in my TEDGlobal talk come from this review article. On average, five years after a diet, most people were back to their original weight. A substantial minority, 41% of dieters, regained more weight than they had lost. And yes, those statistics probably apply to your favorite diet, whatever it is. None of the ones that have been studied have fared better than others in the long term.
In reality, the long-term outcomes are probably worse than that, because such studies are hard to do well. On average, researchers only managed to get follow-up data for a third of the participants after five years. As you might imagine, people who’ve kept the weight off are more likely to respond to such requests than people who’ve gained it all back and then added more pounds. Many studies asked participants to report their own height and weight, which most people underestimate. Finally, researchers often don’t take into account whether participants have been on other diets since the study began. Repeated dieting (weight cycling) can resemble successful weight-loss maintenance if you don’t look too closely.
Losing weight isn’t the hard part. Fighting your brain’s persistent attempts to make you gain it back is a much bigger challenge. And the costs of failure can be high. I’ll have more on that aspect tomorrow.