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unusually strenuous physical exercise slows the rate of loss.” “The patient reasons quite correctly,” Wilder said, “that the more exercise he takes the more fat should be burned and that loss of weight should be in proportion and he is discouraged to find that the scales reveal no progress.”
    The patient’s reasoning had two flaws, as Wilder’s contemporaries would point out. First, we burn surprisingly few caloriesdoing moderate exercise, and, second, the effort can be easily undone, and probably will be, by mindless changes in diet. A 250-pound man will burn
three
extra calories climbing one flight of stairs, as Louis Newburgh of the University of Michigan calculated in 1942. “He will have to climb twenty flights of stairs to rid himself of the energy contained in one slice of bread!”
    So why not skip the stairs and skip the bread and call it a day? After all, what are the chances that if a 250-pounder does climb twenty extra flights a day he won’t eat the equivalent of an extra slice of bread before the day is done?
    Yes, more strenuous exercise will burn more calories—“it really is much more effective to exercise hard enough to sweat,” Kolata tells us, “and that is the only way to burn large numbers of calories”—but, as these physicians argued, it will also make you hungrier still.
    “Vigorous muscle exercise usually results in immediate demand for a large meal,” noted Hugo Rony of Northwestern University in 1940. “Consistently high or low energy expenditures result in consistently high or low levels of appetite. Thus men doing heavy physical work spontaneously eat more than men engaged in sedentary occupations. Statistics show that the average daily caloric intake of lumberjacks is more than 5,000 calories while that of tailors is only about 2,500 calories. Persons who change their occupation from light to heavy work or
vice versa
soon develop corresponding changes in their appetite.” So, if a tailor becomes a lumberjack and, by doing so, takes to eating like one, why assume the same thing wouldn’t happen, albeit to a lesser extent, to an overweight tailor who chooses to work out like a lumberjack for an hour a day? *
    •   •   •
    The dubious credit for why we came to believe otherwise goes almost exclusively to one man, Jean Mayer, who began his professional career at Harvard in 1950, proceeded to become the most influential nutritionist in the United States, and then, for sixteen years, served as president of Tufts University (where there is now a Jean Mayer USDA Human Nutrition Research Center on Aging). Those who have ever believed that they can lose fat and keep it off by exercising have Jean Mayer to thank.
    As an authority on human weight regulation, Mayer was among the very first of a new breed, a type that has since come to dominate the field. His predecessors—Bruch, Wilder, Rony, Newburgh, and others—had all been physicians who worked closely with obese and overweight patients. Mayer was not. His training was in physiological chemistry; he wrote his doctoral thesis at Yale University on the relationship of vitamins A and C in rats. He would eventually publish hundreds of papers on nutrition, including why we get fat, but his job never actually required that he reduce a fat person to a healthy weight, and so his ideas were less fettered by real-life experience.
    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 riding lawn mowers to the electric toothbrush, only serves to reduce 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