Sports Science Update: The Supersize Me Study

A month of pigging out could result in a lifetime of weight gain.

Written by: Matt Fitzgerald

If you haven’t seen it, you’ve at least heard of Supersize Me, the documentary film in which Morgan Spurlock stops exercising and lives on McDonald’s food for one month. The consequences to his health were predictably disastrous. It was hardly a scientific experiment, of course, but one had little doubt that the results of Spurlock’s turn as his own guinea pig were fundamentally truthful.

Now there can be no doubt, as researchers at Sweden’s Linköping University have essentially recreated Spurlock’s experiment in a scientifically rigorous format. But instead of looking at the immediate effects of eating fast food and not exercising, which are indeed too predictable to bother substantiating, they looked at the long-term effects. And based on what they discovered, I wouldn’t be surprised to learn that Morgan Spurlock continues to struggle with his weight today.

In this study, 18 healthy young men and women increased their daily energy intake by roughly 70 percent by pigging out on fast food for a period of four weeks. During the same period, their daily activity was limited to a maximum of 5,000 steps. A control group of matched subjects maintained their normal eating and exercise habits during the four-week period.

As anyone would expect, the fast food eaters gained weight—a lot of weight: some 14 pounds on average. That’s 3.5 pounds a week! Meanwhile the controls gained no weight. But here’s where it gets interesting. Six months later, the reformed fast food eaters had lost about three-quarters of the weight they gained. But after their month of binging, the subjects’ weight had started to creep back up again, and at a 2.5-year follow-up the authors of the study, which was published in the online journal Nutrition & Metabolism, found that, on average, the subjects were nearly seven pounds heavier (all of it in the form of body fat) than they had been before their four weeks of “hyper-alimentation,” as the folks in white coats like to call overeating. The controls did not gain so much as an ounce over that 2.5-year period.

These results suggest that a short period of rapid fat gain could have long-term effects on metabolism that make future weight gain more likely. This finding has a special sort of relevance to runners, who sometimes “let themselves go” a bit during off-season breaks between training periods, confident that they can easily reverse the weight they gain at those times by resuming their training and healthy eating habits. But according to the Supersize Me study, this pattern might not be as harmless as we would like to think. Surely it’s okay and perhaps even unavoidable to fatten up a little bit between marathons, but you’ll want to keep your bodily inflation within a reasonable limit, lest you regret it 2.5 years later.

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Check out Matt’s latest book, RUN: The Mind-Body Method of Running by Feel.