Why dieting doesn't work

By A. Tomiyama

"Everyone knows diets don't work. All they do is stress you out."

This pronouncement, by Oprah Winfrey, characterizes a vast number of women's experiences with dieting: After an initial weight loss, the pounds rebound right back, rendering the entire miserable experience naught. Contrast this with the medical dictum, "calories in, calories out," which argues that reducing one's caloric intake must result in a net loss in calories that necessarily leads to reduced weight.

To physicians, this is biology, and biology is irrefutable. It's also why numerous physicians recommend dieting as a treatment for obesity and why a large body of medical research puts people on low-calorie restrictive diets.

I, along with Traci Mann, associate professor of psychology, and other collaborators, decided a few years ago to determine once and for all whether calorie-restricting diets work.

The issue became particularly important because of a change in the wording in Medicare and Medicaid’s 2004 coverage manual. A simple deletion of the six-word phrase "obesity is not considered an illness" opened the door for Medicare to potentially fund diet-related treatments for obesity. For dieting to cure obesity, it must lead to long-term weight loss. In our review, we focused on every single study (31 in all) in which people were placed on diets and monitored for at least a two-year follow-up period.

We found that participants did tend to lose about 5% to 10% body weight initially. But a majority either regained their entire weight or more weight subsequently. Because research shows that such "yo-yo dieting" is very harmful, we concluded that women may be better off never having gone on a diet in the first place.

Further, we identified several methodological flaws in the studies that may have made the diets appear to be more effective than they were. For example, in many of the studies, participants self-reported their weight or had very low follow-up rates.

Although Medicare should clearly not fund dieting as a treatment for obesity, one question remains: Why doesn't dieting work? Returning to the second half of Oprah's quote &mdash "All they do is stress you out" &mdash it seems that stress might be a plausible reason.

Extensive research suggests that psychological stress can lead to weight gain. And many women would certainly say they find dieting stressful. In fact, 100% of the women in a focus group I conducted said just that.

I hypothesize, therefore, that dieting might result in psychological stress that might, in turn, lead to weight gain and diet failure — a hypothesis I am testing in my dissertation.

It seems irresponsible to assert that "dieting doesn’t work" without offering an alternative. One promising potential solution may be exercise. We found in our study that participants who reported the most exercise were the ones who lost the most weight.

All in all, dieting is an unpleasant experience at best. Given the very strong evidence that regaining weight after dieting is the norm, I hope women will now be free of the tyranny of dieting.

Tomiyama is a doctoral student of social psychology.

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