Good Calories, Bad Calories

But Mayer’s hypothesis always had shortcomings. First, the association between reduced physical activity and obesity doesn’t tell us what is cause and what is effect. “It is a common observation,” noted Hugo Rony, “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.” It’s also possible that both obesity and physical inactivity are the symptoms of the same underlying cause. This was a likely explanation for the inactivity and obesity that Mayer had observed in his laboratory mice. The same genetic mutation that rendered these mice sedentary could also have induced obesity (and perhaps diabetes).

Another problem, as we discussed in the last chapter, is that obesity is also associated with poverty, and even extreme poverty, and that should be a compelling argument against physical inactivity as a cause of the disease. Those who earn their living through manual labor tend to be the less advantaged members of societies in developed nations, and yet they will have the greatest obesity rates.

A third problem was the observation that exercise accomplishes little in the way of tilting the caloric balance when compared with a very modest restriction of intake—walking a few miles as opposed to eating one less slice of bread—and that increasing activity will increase appetite. Mayer ignored the comparison of intake and expenditure by focusing on expenditure alone. “For a long period the role of exercise in weight control was disregarded, if not actually ridiculed,” he wrote in a 1965 New York Times Magazine article. “One reason often advanced for this neglect is that ‘exercise consumes very little energy.’…Somehow the impression was given that any such exercise had to be accomplished in a single uninterrupted session. Actually, exercise does correspond to a caloric expenditure that can be considerable, and this expenditure will take place in a day or a decade.” And so the expenditure of calories by exercise, no matter how small, according to Mayer, would accumulate, leading to long-term weight reduction. This, of course, would be true only if the excess expenditure went unaccompanied by a compensatory increase in appetite and intake.

Mayer acknowledged that exercise could increase food intake, but said it wasn’t “necessarily” the case. This was the heart of Mayer’s hypothesis—a purported loophole in the relationship between appetite and physical activity. “If exercise is decreased below a certain point,” Mayer told the New York Times 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….” Mayer based this conclusion on two of his own studies from the mid-1950s.^*78 The first was with laboratory rats and purported to demonstrate that rats that are exercised for one to two hours every day will actually eat less than rats that don’t exercise at all. The second was a study of mill workers in West Bengal, India, and stands as a reminder that dreadful science can pass for seminal research in the field of obesity.

Mayer worked with the dietician and chief medical officer of the company that owned the Bengali mill and an accompanying bazaar, and it was these Indian colleagues who assessed the physical activity and diet of the resident workers. These men, as Mayer reported, ranged from “extraordinarily inert” stall holders “who sat at their shop all day long,” to those engaged in intense physical activity who “shoveled ashes and coal in tending furnaces all day long.”

The evidence reported in Mayer’s paper could have been used to demonstrate any point. The more active workers in the mill, for example, both weighed more and ate more. As for the sedentary workers, the more sedentary they were, the more they ate and the less they weighed. The twenty-two clerks who lived on the premises and sat all day long weighed ten to fifteen pounds less and were reported to have eaten four hundred calories more on average than the twenty-three clerks who had to walk three to six miles to work, or even than those five clerks who walked to work and played soccer every day.

Nonetheless, Mayer claimed that the study confirmed the findings of his rat experiment. He based his conclusion exclusively on the relative girth of thirteen stallholders and eight supervisors. These men weighed, respectively, fifty to sixty pounds and thirty to forty pounds more than the clerks who worked for them, and yet, according to Mayer’s data, consumed the same amount of calories. Mayer implied that they added this extra weight because they were somehow even less active than those employees whose jobs entailed sitting all day, but he had no evidence for it. It’s also possible that their relative wealth introduced other dietary factors that could have explained the dramatic differences in weight. Either way, as John Garrow noted, these findings would never be replicated, which is why such authorities as the Institute of Medicine of the National Academies of Science still cite Mayer’s study today as the only evidence for the proposition that “too little” exercise can disrupt the mechanisms that normally regulate food intake.

Mayer’s advocacy of exercise for weight control did not go unchallenged. After his 1965 New York Times Magazine article, entitled “The Best Diet Is Exercise,” physicians working with obese patients wrote to the newspaper saying that Mayer’s faith in exercise was unreasonable and flouted common sense. “As much as Dr. Mayer minimizes the thirst and appetite increases after exercise, my patients all seem to be thirstier after tennis and find it difficult to stick to plain water,” wrote Morton Glenn of New York University College of Medicine; “and who hasn’t heard someone say: ‘This walk all the way home sure gave me an appetite!’ Exercise can and does increase thirst and appetite, in most persons, in most situations, and most people respond to these sensations accordingly!”

Despite these commonsensical objections, Mayer’s hypothesis won out. It helped that Mayer—like Ancel Keys and Dennis Burkitt—perceived the process of convincing the public and the medical-research community to be akin to a crusade. This served to absolve him, apparently, of the obligation to remain strictly accurate about what the research, including his own, had or had not demonstrated. In the popular press, Mayer would unleash his less scientific impulses. He wrote about the “false idea which continues to have broad and pernicious acceptance” that exercise would increase appetite, and he insisted that the “facts overwhelmingly demonstrate” that this was “not necessarily” the case.

As Mayer’s political influence grew through the 1960s, his prominence and his proselytizing contributed to the belief that his hypothesis had both been proven true and was widely accepted. In 1966, when the U.S. Public Health Service advocated increased physical activity and diet as the best ways for us to lose weight, Mayer was the primary author of the report. Three years later, Mayer chaired Richard Nixon’s 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, Mayer began writing a syndicated newspaper column on nutrition that clearly did not hold to the standards of a serious scientific publication. Sounding suspiciously like a diet doctor selling a patent claim, Mayer said that exercise “makes weight melt away faster.” “Contrary to popular belief,” Mayer asserted, “exercise won’t stimulate your appetite.”

The current culture of physical exercise in the United States emerged in the late 1960s, coincident with Mayer’s crusade and accompanied by a media debate about whether exercise is or is not good for us. “While it is generally agreed that exercise programs can improve strength, stamina, coordination and flexibility and provide an overall sense of well-being, two crucial questions remain,” a 1977 New York Times Magazine article observed: “(1) Does exercise prolong life? and (2) does it give any protection against the modern scourge, heart disease?” A handful of observational studies had linked exercise to greater longevity—the most famous being a study of seventeen thousand Harvard alumni published by Ralph Paffenbarger in 1978—but these didn’t reveal whether this effect was due to the health benefits of exercise or the fact that healthier people are more likely to exercise. Those who exercised regularly also tended to smoke less and pay more attention to their diets.