Beware of samples of one

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We all know that if you live on McDonald’s hamburgers for a month you’ll turn grossly obese, your “bad” cholesterol level will zoom and your liver will deteriorate.

We know it because we saw it with our own eyes in Morgan Spurlock’s documentary Super Size Me. The movie made such a yucky splash that it won the best director’s prize at the Sundance Film Festival as well as an Academy Award nomination, and supposedly led McDonald’s to end its “super size” promotion.

The film also caught the attention of Fredrik Nyström, MD, PhD, an associate professor in the department of endocrinology and metabolism at the Linköping University Hospital in Sweden. Realizing that previous studies on obesity had been done on patients who were overweight to begin with, he saw an opportunity to study what weight gain would do in non-obese people, and so he decided to duplicate the Spurlock diet in an experiment with scientific controls.

“I thought Spurlock had a good idea to combine excess calories with reduced physical activity for a limited time,” said Nyström (who is also secretary of the Swedish Society of Hypertension) in an e-mail. That is why he recruited 18 healthy, normal weight volunteers to go on a comparable diet of 6,600 calories per day for a month.

He had no trouble signing up male students in their early 20s, who welcomed the chance to let the university pay them to stuff themselves with junk food and provide free bus passes, since walking or bicycling were taboo. Female students proved more reluctant to get fat, and so the final sample consisted of 12 men but only six women.

But a funny thing happened on the way to the vomitorium: none of the 18 study subjects suffered Spurlock’s devastating results. Nyström conducted weekly metabolic, physical and mental tests (Spurlock also suffered from depression during his experiment), but with the exception of one student who quickly gained the 15% the ethics committee had set as the safe maximum, no one else had to be taken off the study.

 Nyström is still working on his official publication but, he reported, none of his subjects deteriorated like Spurlock. Despite the fact that all experienced the expected weight gain, “some subjects increased basal metabolic rate by 30% in just two weeks of the diet, meaning that they produced extra [body] heat of one complete hamburger per day.” Furthermore, “the deterioration of Spurlock’s lipid levels does not fit at all with any of my 18 participants,” and some levels actually improved, while liver function—after initially deteriorating—began to recover by the third week.

Asked whether he has any theories as to why Spurlock reacted so differently from his students, Nyström ventured, “Perhaps he has some sort of disease?”

In an article in New Scientist he is quoted as saying that as he “teases out the huge amount of data” he accumulated, he hopes to be able “to identify new approaches to tackling the obesity epidemic,” because he now suspects that the overweight problem isn’t as straightforward as has been thought.

Before you go raid the refrigerator, however, consider that you might have Spurlock’s metabolism and not that of Swedish students in their 20s.

Warren Ross is MM&M’s editor at large

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