The belief in physical activity as a method of weight control is relatively new, however, and it has long been contradicted by the evidence. When Russell Wilder of the Mayo Clinic lectured on obesity in 1932, he noted that his patients tended to lose more weight with bed rest, “while 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.”

Until the 1960s, clinical investigators routinely pointed out that moderate exercise would lead only to insignificant increases in energy expenditure, and these could be easily matched by slight and comparatively effortless changes in diet. A 250-pound man will expend three extra calories climbing a flight of stairs, as Louis Newburgh of the University of Michigan calculated in 1942, and this in turn is the equivalent of depriving himself of one-fourth of a teaspoon of sugar or a tenth of an ounce of butter. “He will have to climb twenty flights of stairs to rid himself of the energy contained in one slice of bread!” Newburgh observed.

Though more strenuous exercise would burn more calories, it would also lead to a significant increase in appetite. This is the implication of the phrase “working up an appetite.” “Vigorous muscle exercise usually results in immediate demand for a large meal,” noted the Northwestern University endocrinologist Hugo Rony 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.”*77 If a tailor became a lumberjack and, by doing so, took to eating like one, there was little reason to think that the same wouldn’t happen, albeit on a lesser scale, to an obese tailor who chose to work out like a lumberjack for an hour a day. In 1960, when the epidemiologist Alvan Feinstein examined the efficacy of various obesity treatments in a lengthy review in the Journal of Chronic Diseases, he dismissed exercise in a single paragraph. “There has been ample demonstration that exercise is an ineffective method of increasing energy output,” Feinstein noted, “since it takes far too much activity to burn up enough calories for a significant weight loss. In addition, physical exertion may evoke a desire for food so that the subsequent intake of calories may exceed what was lost during the exercise.”