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.