Good Calories, Bad Calories

of Medicine in Boston, and who entitled his article, for just this reason, “The Myth of Diet in the Management of Obesity.” “There is no investigator who has looked for this effect and failed to find it,” the British obesity researcher John Garrow wrote in 1978.

The latest reiteration of these experiments, using obese subjects, was conducted by Jules Hirsch at Rockefeller University, and the results were published in The New England Journal of Medicine in 1995. Calorie restriction in Hirsch’s experiment resulted in disproportionate reductions in energy expenditure and metabolic activity. Increasing calorie consumption resulted in disproportionate increases in metabolic activity.

Hirsch and his colleagues interpreted their observations to mean that the human body seems surprisingly intent on maintaining its weight—resisting both weight gain and weight loss—so that the obese remain obese and the lean remain lean. As Hirsch explained it, the obese individual appears to be somehow metabolically normal in the obese state, just as Keys’s and Benedict’s young men were metabolically normal in their lean or overweight states before their semi-starvation diets. Once Hirsch’s obese subjects took to restricting their calories, however, they experienced what he called “all the physiological and psychological concomitants of starvation.” A semi-starvation diet induces precisely that—semi-starvation—whether the subject is obese or lean. “Of all the damn unsuccessful treatments,” Hirsch later said, “the treatment of weight reduction by diet for obese people just doesn’t seem to work.”

Over the course of a century, a paradox has emerged. Obesity, it has been said, is caused, with rare exceptions, by an inability to eat in moderation combined with a sedentary lifestyle. Those of us who gain excessive weight consume more calories than we expend, creating a positive caloric balance or a positive energy balance, and the difference accumulates as excessive pounds of flesh. But if this reconciles with the equally “indisputable” notion that “eating fewer calories while increasing physical activity are the keys to controlling body weight,” as the 2005 USDA Dietary Guidelines for Americans suggest, then the problems of obesity and the obesity epidemic should be easy to solve. Those few individuals for whom obesity is a preferred condition, such as sumo wrestlers, would remain obese through their voluntary program of overeating, and the rest would create a negative energy balance, lose the excess weight, and return to leanness. The catch, as Hirsch pointed out, is that this doesn’t happen.

The documented failure of semi-starvation diets for the obese dates back at least half a century. It begins with Albert Stunkard’s analysis of the relevant research in the mid-1950s, motivated by his desire to resolve what he called the “paradox” between his own failure to reduce obese patients successfully by diet at New York Hospital and “the widespread assumption that such treatment was easy and effective.” Stunkard managed to locate eight reports in the literature that allowed for an accurate assessment of whether semi-starvation diets worked. In 1959, he reported that the existing evidence confirmed his own failures: semi-starvation diets were “remarkably ineffective” as a treatment for obesity. Only 25 percent of the subjects discussed in these articles had lost as much as twenty pounds on their semi-starvation diets, “a small weight loss for the grossly overweight persons who are the subjects of these reports.” Only 5 percent successfully lost forty pounds. As for Stunkard’s own experience with a hundred obese patients, all prescribed “balanced” diets of eight to fifteen hundred calories a day, “only 12% were able to lose 20 lb., and only 1 patient lost 40 lb….Two years after the end of treatment only two patients had maintained their weight loss.”^*76

A decade later, when Stunkard was invited to discuss obesity at Richard Nixon’s White House Conference on Food, Nutrition, and Health, he had come to believe that the adverse effects caused by semi-starvation diets as a treatment for obesity often outweighed any benefits. “Attempts at weight reduction are often accompanied by anxiety and depression, at times severe enough to warrant discontinuation,” he said. “Many obese persons today might well be better off if they learned to live with their condition and stopped subjecting themselves over and over to painful and frustrating attempts to lose weight.”

More recent assessments of the efficacy of semi-starvation diets tend to be studies that set out to evaluate the efficacy of low-fat, calorie-restricted diets, but because they do so by comparing these diets with more balanced calorie-restricted diets, they provide evidence for the efficacy of the latter as well. In 2002, a Cochrane Collaboration review of the evidence concluded that low-fat diets induced no more weight loss than calorie- restricted diets, and in both cases the weight loss achieved “was so small as to be clinically insignificant.” A similar analysis was published in 2001 by the U.S. Department of Agriculture. In this case, the authors identified twenty- eight relevant trials of low-fat diets, of which at least twenty were also calorie-restricted. The overweight subjects consumed, on average, less than seventeen hundred calories a day for an average weight loss of not quite nine pounds over six months. Only one of these studies tracked its participants for more than a year, and in that case the subjects reportedly reduced their caloric intake to thirteen hundred calories for eighteen months. In other words, these subjects reportedly consumed fewer calories per day than had Keys’s conscientious objectors, they maintained this semi-starvation regimen for three times as long—and they emerged from the trial having gained, on average, a pound. In the Women’s Health Initiative, discussed earlier (see Chapter 4) twenty thousand women were prescribed a low-fat diet and reportedly reduced their calorie consumption by an average of 360 calories a day. After almost eight years of this regimen, they weighed only two pounds less than when they started, and their average waist circumference, which is a measure of abdominal fat, had increased.

The evidence for the failure of semi-starvation as a treatment of obesity hasn’t stopped obesity researchers from recommending the approach. The Handbook of Obesity, published in 1998 and edited by three of the most prominent authorities in the field—George Bray, Claude Bouchard, and W.P.T. James— says that “dietary therapy remains the cornerstone of treatment and the reduction of energy intake continues to be the basis of successful weight reduction programs.” It also notes, in contradiction, that the results of such calorie- restricted diets “are known to be poor and not long-lasting.” The chapter on obesity in the latest edition of Joslin’s Diabetes Mellitus, written by two clinical investigators from Harvard Medical School, also describes “reduction of caloric intake” as “the cornerstone of any therapy for obesity.” It then notes that reducing energy intake to a level substantially below that of energy expenditure “is difficult to accomplish despite a wide variety of specific dietary approaches.” A deficit of seventy-five hundred calories, the authors explain, “is predicted to produce a weight loss of [2.2 pounds],” and so a reduction in food intake of a hundred calories a day “should bring about [an eleven-pound] weight loss over 1 year.” But this doesn’t seem to happen. “It is clear from common experience, however, that attempts at dieting that rely on such small reduction in food intake are rarely successful. Thus, more severe reductions in energy intake are typically prescribed,” the Harvard physicians write. These more severe regimens include total starvation, but “the extreme nature of the therapy,” the loss of muscle rather than fat tissue, and the many complications “have led to the virtual disappearance of this approach.” They also include very low-calorie diets of two to six hundred calories a day, which will inevitably lead to weight loss, but the weight loss diminishes as the diet progresses, once again because metabolism and energy expenditure both decrease, and when the patients go off the diet, they regain the weight lost. Finally, there are the “many different diets” that provide eight hundred to a thousand calories and are in common use, all of which “should result in weight loss.” “None of these approaches,” the authors say, “has any proven merit.”

In response to these pessimistic assessments, it is commonly suggested that the obese would ameliorate their problem, or prevent it, if they merely exercised—perhaps sixty or ninety minutes a day, as now prescribed by the USDA Dietary Guidelines. A negative energy balance can be created, according to this logic, by increasing energy expenditure as well as by eating less. Advice to engage in daily physical activity is now ever-present in public-health messages and popular writing on the problems of obesity and overweight. It’s reinforced by the existence of the ubiquitous electronic displays on stair-climbers, treadmills, and other exercise apparatus that tell us how many calories we allegedly expended in our latest workout.