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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 actually began extolling exercise as a means of weight control in the early 1950s, a few years out of graduate school, afterstudying a strain of obese mice that had a surprisingly small appetite. This seemed to absolve eating too much from being the cause of their obesity, so Mayer naturally assumed their sedentary behavior must be responsible, and they were certainly sedentary. They barely moved. By 1959,
The New York Times
was giving Mayer credit for having “debunked” the “popular theories” that exercise was of little value in weight control, which he hadn’t.
    Mayer acknowledged that appetite tended to increase with physical activity, but the heart of his argument was that it wasn’t “necessarily” the case. He believed there was a loophole in the relationship between expending more energy and eating more as a result. “If exercise is decreased below a certain point,” Mayer explained in 1961, “food intake no longer decreases. 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.” So, if you’re sufficiently sedentary, you’re going to eat just as much as you would if you were a little active and expended more energy.
    Mayer based this conclusion on two (and only two) of his own studies from the mid-1950s.
    The first was on laboratory rats, purporting to demonstrate that when these rats were forced to exercise for a few hours every day, they ate less than rats that didn’t exercise at all. Mayer didn’t say that they actually weighed less, only that they ate less. As it turns out, rats on these exercise programs eat more on days when they aren’t forced to run and will expend less energy when they’re not exercising. Their weights, however, remain the same as those of sedentary rats. And when rats are retired from these exercise programs, they eat more than ever and gain weight with age more rapidly than rats that are 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 weight 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, would never be 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. And as Mayer’s political influence grew through the 1960s, this contributed to the appearance that his faith in the weight-reducing benefits of exercise was widely shared. In 1966, when the U.S. Public Health Service first advocated dieting
and
increased physical activity as the keys to weight loss, Mayer wrote the report. Three years later, he chaired a White House Conference on Food, Nutrition and Health. “The successful treatment of obesity must involve far reaching changes in life style,” the conference report concluded. “These changes include alterations of dietary patterns and physical activity.” In 1972, when Mayer began writing a syndicated newspaper column on nutrition, he came across like a diet doctor selling a patent claim. Exercise, he wrote, would “make weight melt away faster,” and, “contrary to popular belief, exercise won’t stimulate your appetite.”
    Meanwhile, the evidence never supported Mayer’s hypothesis—not in animals, as I said, and certainly not in humans. One remarkable study of the effect of physical activity on weight