Why We Get Fat: And What to Do About It (8 page)

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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 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, after
studying 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,
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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.
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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 loss was published in 1989 by a team of Danish researchers. The Danes actually did train sedentary subjects to run marathons (26.2 miles). After eighteen months of training, and after actually running a marathon, the eighteen men in the study had lost an average of five pounds of body fat. As for the nine women subjects, the Danes reported, “no change in body composition was observed.” That same year, Xavier Pi-Sunyer, director of the St. Luke’s-Roosevelt Hospital Obesity Research Center in New York, reviewed the existing trials testing the notion that increasing exercise would lead to weight loss. His conclusion was identical to that of the Finnish review in 2000: “Decreases, increases, and no changes in body weight and body composition have been observed.”

We bought into the idea that we could exercise more and not compensate by eating more because the health reporters bought it, and their articles in the lay press were widely read. The research literature itself was not.

In 1977, for instance, in the midst of the exercise explosion, the National Institutes of Health hosted its second ever conference on obesity and weight control, and the assembled experts concluded that “the importance of exercise in weight control is less than might be believed, because increases in energy expenditure due to exercise also tend to increase food consumption, and it is not possible to predict whether the increased caloric output will be outweighed by the greater food intake.” That same year, the
New York Times Magazine
reported that there was “now strong evidence that regular exercise can and does result in substantial and—so long as the exercise is continued—permanent weight loss.”
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By 1983, Jane Brody, personal-health reporter for the
Times
,
was counting the numerous ways that exercise was “the key” to successful weight loss. By 1989, the same year Pi-Sunyer gave his pessimistic assessment of the actual evidence,
Newsweek
declared exercise an “essential” element of any weight-loss program. Now, according to the
Times
, on those infrequent occasions “when exercise isn’t enough” to induce sufficient weight loss, “you must also make sure you don’t overeat.”

Why the obesity researchers and public-health authorities eventually came to believe this story is a different question. Umberto Eco offered a likely answer in his novel
Foucault’s Pendulum
. “I believe that you can reach the point,” Eco wrote, “where there is no longer any difference between developing the habit of pretending to believe and developing the habit of believing.”

From the late 1970s onward, the primary factor fueling the belief that we can maintain or lose weight through exercise seemed to be the researchers’ desire to believe it was true and their reluctance to acknowledge otherwise publicly. Although one couldn’t help being “underwhelmed” by the actual evidence, as Judith Stern, Mayer’s former student, wrote in 1986, it would be “shortsighted” to say that exercise was ineffective, because it meant ignoring the
possible
contributions of exercise to the prevention of obesity and to the maintenance of any weight loss that might have been induced by diet. These, of course, had never been demonstrated, either.

This philosophy came to dominate even the scientific discussions of exercise and weight, but it couldn’t be reconciled with the simple notion that appetite and the amount we eat can be expected to increase the more we exercise. And so the idea of working up an appetite was jettisoned along the way. Physicians, researchers, exercise physiologists, even personal trainers at the gym took to thinking about hunger as though it were something that existed only in the brain, a question of willpower (whatever that is), not the natural consequence of a body’s effort to get back the energy it has expended.

As for the researchers themselves, they invariably found a way to write their articles and reviews that allowed them to continue to promote exercise and physical activity, regardless of what the evidence actually showed. One common method was (and still is) to discuss only the results that seem to support the belief that physical activity and energy expenditure can determine how fat we are, while simply ignoring the evidence that refutes the notion, even if the latter is in much more plentiful supply.

Two experts in the
Handbook of Obesity
, for instance, reported as a reason to exercise that the Danish attempt to turn sedentary subjects into marathon runners had resulted in a loss of five pounds of body fat in male subjects; they neglected to mention, however, that it had zero influence on the women in the trial, which could be taken as a strong incentive not to exercise. (If your goal is to lose weight—even if your health and your life depend on it, as they very well may—would you train to run a twenty-six-mile foot race upon being told that you
might
lose five pounds of fat after a year and half of work?)

Other experts took to arguing that we could lose weight by weightlifting or resistance training rather than the kind of aerobic activity, like running, that was aimed purely at increasing our expenditure of calories. The idea here was that we could build muscle and lose fat, and so we’d be fitter even if our weight remained constant, because of the trade-off. Then the extra muscle would contribute to maintaining the fat loss, because it would burn off more calories—muscle being more metabolically active than fat.

To make this argument, though, these experts invariably ignored the actual numbers, because they, too, are unimpressive. If we replace five pounds of fat with five pounds of muscle, which is a significant achievement for most adults, we will increase our energy expenditure by two dozen calories a day. Once again, we’re talking about the caloric equivalent of a quarter-slice of bread, with no guarantee that we won’t be two-dozen-calories-a-day hungrier because of this. And once again we’re back to the
notion that it might be easier just to skip both the bread and the weightlifting.

Before I finish this discussion of exercise and energy expenditure, I want to return briefly to the guidelines published in August 2007 by the American Heart Association and the American College of Sports Medicine. “It is reasonable to assume that persons with relatively high daily energy expenditures would be less likely to gain weight over time, compared with those who have low energy expenditures,” the expert authors had written. “So far, data to support this hypothesis are not particularly compelling.”

Damaging as this may be to the notion that we can lose weight by exercising, the authors were unwilling to be definitive. They had slipped in a qualification, the words “so far.” By doing so, they were leaving the door of possibility open. Maybe somebody, someday, would show scientifically that what these experts believed in their hearts to be true really was.

But they missed the point with their qualification. Here it is: this idea that we get fat because we’re sedentary and we can get lean or prevent ourselves from fattening further by upping our energy expenditure is at least a century old. One of the most influential European authorities on obesity and diabetes, Carl von Noorden, suggested this in 1907. We can, in fact, trace it to the 1860s, when the obese British undertaker William Banting discussed his numerous failed attempts to lose weight in his best-selling
Letter on Corpulence
. A physician friend, wrote Banting, suggested he slim down by “increased bodily exertion.” So Banting took up rowing “for a couple of hours in the early morning.” He gained muscular vigor, he wrote, “but with it a prodigious appetite, which I was compelled to indulge, and consequently increased in weight, until my kind old friend advised me to forsake the exercise.”

The experts from the AHA and the ACSM would like to think that maybe if we just put further effort into studying the relationship
between exercise and weight—if we do the experiments in just the right ways—we will finally confirm what von Noorden and Banting’s physician friend and a century of researchers and physicians and exercise aficionados ever since have argued somehow must be true.

The history of science suggests another interpretation: if people have been thinking about this idea for more than a century and trying to test it for decades and they still can’t generate compelling evidence that it’s true, it’s probably not. We can’t say it’s not with absolute certainty, because science doesn’t work that way. But we can say that there’s now an exceedingly good chance it’s simply wrong, one of the many seemingly reasonable ideas in the history of science that never panned out. And if reducing calories-in doesn’t make us lose weight, and if increasing calories-out doesn’t even prevent us from gaining it, maybe we should rethink the whole thing and find out what does.