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The Scientist and the Stairmaster

Through the sixties, Mayer documented the relationship between inactivity and the overweight. He noted that fat high-school girls ate “several hundred calories less” than lean classmates. “The laws of thermodynamics were, however, not flouted by this finding,” he wrote, because the obese girls expended less energy than the lean: They were much less active; they spent four times as many hours watching television. Mayer also studied infants. “The striking phenomenon is that the fatter babies were quiet, placid babies that had moderate intake,” Mayer reported, “whereas the babies who had the highest intake tended to be very thin babies, cried a lot, moved a lot, and became very tense.” Thus, Mayer concluded, “some individuals are born very quiet, inactive, and placid and with moderate intake get fat, and some individuals from the very beginning are very active and do not get particularly fat even with high intakes.”

It was Mayer who pioneered the now-ubiquitous practice of implicating sedentary living as the “most important factor” leading to obesity and the chronic diseases that accompany it. Modern Americans, said Mayer, were inert compared with their “pioneer forebears” who were “constantly engaged in hard physical labor.” Every modern convenience, by this logic, from power windows to the electric toothbrush, only serves to minimize the calories we expend. “The development of obesity,” Mayer wrote in 1968, “is to a large extent the result of the lack of foresight of a civilization which spends tens of billions annually on cars, but is unwilling to include a swimming pool and tennis courts in the plans of every high school.”

Mayer’s hypothesis always had shortcomings, but they were ignored for the same reasons they still are—who wants to openly question the idea that physical activity is a panacea? The first issue is a logical one: That conclusion that the fatter we are, the more sedentary we’re likely to be is actually a correlation; it tells us nothing about what is cause and what is effect. “It is a common observation,” noted Rony in 1941, “that many obese persons are lazy, i.e., show decreased impulse to muscle activity. This may be, in part, an effect that excess weight would have on the activity impulse of any normal person.” Equally possible is that obesity and physical inactivity are both symptoms of the same underlying cause.

The one thing that might be said about exercise with certainty is that it tends to make us hungry. Maybe not immediately, but eventually. Burn more calories and the odds are very good that we’ll consume more as well.

This logical problem was then obscured by Mayer’s all-out attack on the role of hunger. Mayer acknowledged that exercise could make us hungrier, but he said it wasn’t necessarily the case. This was the heart of Mayer’s message—a purported loophole in the relationship between appetite and physical activity. “If exercise is decreased below a certain point, food intake no longer decreases,” said Mayer. “In other words, walking one half-hour a day may be equivalent to only four slices of bread, but if you don’t walk the half-hour, you still want to eat the four slices.”

Mayer based this conclusion on two (and only two) of his own studies from the mid-fifties. The first purported to demonstrate that laboratory rats exercised for a few hours every day will eat less than rats that don’t exercise at all. But this would never be replicated. In more recent experiments, the more rats run the more rats eat; weights remain unchanged. And when rats are retired from these exercise programs, they eat more than ever and gain weight with age more rapidly than rats that were allowed to remain sedentary. With hamsters and gerbils, exercise increases body weight and body-fat percentage. So exercising makes these particular rodents fatter, not leaner.

Mayer’s second study was an assessment of the diet, physical activity, and weights of workers and merchants at a mill in West Bengal, India. This article is still cited—by the Institute of Medicine, for instance—as perhaps the only existing evidence that physical activity and appetite do not necessarily go hand in hand. But it, too, has never been replicated, despite (or perhaps because of) a half-century of improvements in methods of assessing diet and energy expenditure in humans.

It helped that Mayer promoted his pro-exercise message with a fervor akin to a moral crusade. In 1966, Mayer was the primary author of a U.S. Public Health Service report advocating increased physical activity along with diet as the best way to lose weight. In 1969, Mayer chaired Richard Nixon’s White House Conference on Food, Nutrition, and Health. “The successful treatment of obesity must involve far-reaching changes in lifestyle,” the conference report concludes. “These changes include alterations of dietary patterns and patterns of physical activity.” In 1972, Mayer began writing a syndicated newspaper column on nutrition: Exercise, Mayer now wrote, sounding suspiciously like a diet doctor selling a patent claim, will make “weight melt away faster,” and “contrary to popular belief, exercise won’t stimulate your appetite.”