Good Calories, Bad Calories

recent studies, in which she had put obese young men on eighteen-hundred-calorie diets with the protein content fixed at 460 calories (26 percent), but with varying proportions of fat and carbohydrates. Over the course of nine weeks, she reported, “weight loss, fat loss, and percent weight loss as fat appeared to be inversely related to the level of carbohydrate in the diets”—in other words, the fewer carbohydrates and the more fat in the diet, the greater the weight loss and the greater the fat loss. “No adequate explanation could be given for the differences in weight losses,” she said. All of the carbohydrate-restricted diets, she said, “gave excellent clinical results as measured by freedom from hunger, allaying of excessive fatigue, satisfactory weight loss, suitability for long term weight reduction and subsequent weight control.”

The last of these conferences to be held before the nutritional wisdom began to shift definitively was in London in December 1973, just two months after the NIH meeting. This one was organized by Yudkin, and many of those giving presentations had also attended the NIH conference. Their presentations were similar, but here there was more of a tendency to implicate carbohydrates specifically as the cause of obesity. Lester Salans and Edward Horton, both collaborators of Ethan Sims on his experimental obesity studies, discussed the effect of carbohydrates on hyperinsulinemia and the role of hyperinsulinemia in obesity. “It is clear that in both lean and obese subjects the carbohydrate content of the diet influences…insulin and glucose concentrations,” Horton reported. He added that it was probably hyperinsulinemia that induced both obesity and insulin resistance. Yudkin then gave the only talk on dietary therapy, entitled “The Low-Carbohydrate Diet,” noting that these diets are higher in vitamins and minerals than calorie-restricted diets, simply because the foods restricted—starches and sugars—have few or no vitamins and minerals. The diet will “reduce superfluous adiposity,” Yudkin said, “but it will not need to be changed when this has been done…. The diet is intended as anew but permanent pattern of eating and not simply as a cure for obesity, to be abandoned when an acceptable loss of weight is achieved.” Harry Keen, who was then at Guy’s Hospital Medical School and would become one of the most influential diabetologists in the U.K.,^*122 said the critical issue wasn’t just obesity, but the chronic diseases that accompanied it. “With the chronically failed case of obesity we are dealing with the wreckage of the situation,” he said, so it was necessary to set “new patterns of body weight and body size, if we are going to make a serious attempt to reduce the frequency, for example, of atherosclerosis, of diabetes mellitus and of a number of other conditions.” Keen and his colleagues had tested the viability of this goal, he reported, on a group of “ostensibly normal men in whom obesity is represented no more frequently than in the population at large.” These men were instructed to restrict their carbohydrate intake to less than five hundred calories a day, but to continue eating protein and fat as desired. The result was an average weight loss of fourteen pounds, impressive because these individuals were not necessarily overweight to begin with. That weight loss had been maintained for almost five years. To those who might be pessimistic about the prevention of obesity and overweight in the public at large, Keen said, this result should be taken as “a word of reassurance and optimism.”

By 1972, The New York Times Natural Foods Dieting Book was offering both a low- calorie weight-loss plan, at a thousand calories a day, and a low-carbohydrate method. “You strictly curtail the amount of carbohydrates you eat daily,” the book explained. “You eat, instead, foods in which the carbohydrate content is very low or nonexistent. Meat…fish, poultry, fats, butter, most cheeses and eggs are equally low in that fattening substance, and these are the foods that form the basis for your diet…for without carbohydrates you cannot gain weight!”

Two years later, when the nonprofit organization Consumer Guide published its first edition of Rating the Diets, a 380-page compendium of the pros and cons of popular diets, carbohydrate restriction seemed firmly established in the canon. Rating the Diets, which obesity authorities would repeatedly recommend as a valuable review of the evidence, concluded that a diet including less than sixty grams of carbohydrates each day had “much to recommend it” and so was “helpful and beneficial” for weight loss. It also quoted a medical textbook to the effect that “the difficult-to-treat obese patient,” which effectively means every obese patient, “appears to suffer from some defect in dealing with carbohydrate which leads to an unnatural conversion of it to fat and to storage of the fat. Avoidance of too much dietary carbohydrate reduces this tendency.” The only caveat with these diets, according to Rating the Diets, was that they “pay little attention to the kinds of fats you eat” and so might increase heart-disease risk.

The shift in the nutritional wisdom was now taking place, driven by the contagious effect of Ancel Keys’s dietary-fat/heart-disease hypothesis on the closely related field of obesity. Any diet that allowed liberal fat consumption was to be considered unhealthy. Clinical investigators working on the problem of human obesity concurred.

Through the 1950s, the carbohydrate-restricted diet had challenged only the positive-caloric-balance hypothesis of obesity. Yudkin had managed to reconcile carbohydrate restriction with this conventional wisdom by insisting that low-carbohydrate diets were low-calorie diets in disguise. By doing so, Yudkin made the diets politically acceptable, although he also directed attention away from the underlying science. In the same 1960 Lancet article in which Yudkin proclaimed what he called “the inevitability of calories,” he had made the point that if the diet was indeed low in calories, then its fat content would also be comparatively low, reconciling his diet with Keys’s dietary-fat hypothesis. This was Yudkin’s “no bread, no butter” argument. If carbohydrate calories are restricted, fat calories are, too. Though the proportion of fat in the diet increases if carbohydrates are avoided, the absolute quantity of fat may actually decrease. This is why Yudkin insisted that the correct terminology for these diets should be “low-carbohydrate” rather than “high-fat.” “It is highly implausible,” Yudkin wrote in 1974, “that a given amount of fat that is harmless when energy intake is excessive becomes harmful when this excess is corrected by a reduction in the intake of sugar and starch.”

As a result of Yudkin’s conciliatory efforts, the only carbohydrate-restricted diets that elicited a backlash from nutritionists were those promoted by clinicians whose interpretation of the science disagreed with Yudkin’s. This situation was exacerbated by the fact that it was these physicians, without university affiliations, who adopted the diet quickly and then wrote books for the lay public that sold exceptionally well. Because their claims sounded like quackery—The High-Calorie Way to Stay Thin Forever, as Dr. Atkins’ Diet Revolution was subtitled—they were treated as such, and particularly so after the medical and public-health authorities decided that dietary fat might cause heart disease.

The small contingent of influential nutritionists from Fred Stare’s department at Harvard provide an example of how this process of entrenchment evolved. In 1952, when Alfred Pennington lectured at Harvard on the benefits of carbohydrate restriction and Keys was only beginning his crusade against dietary fat, Mark Hegsted had suggested, “Dr. Pennington may be on the right track in the practical treatment of obesity.” A decade later, and a year after the American Heart Association had officially sided with Keys, the Brooklyn obstetrician Herman Taller published his best-seller, Calories Don’t Count, based on Pennington’s work and Taller’s clinical experiences with the diet. Stare called the book “trash,” and Jean Mayer described the high-fat aspect of the diet as “potentially dangerous.” Philip White, who received his doctorate in nutrition from Stare’s department, then wrote a review of Calories Don’t Count for JAMA, accusing Taller of perpetrating “nutrition nonsense and food quackery.” In 1973, in response to the publication of Dr. Atkins’ Diet Revolution, based on Atkins’s clinical experience with overweight patients and another decade of science, White edited a critique of carbohydrate-restricted diets in JAMA—the first draft of which was written by Ted Van Itallie, another veteran of Stare’s nutrition department—that now dismissed the diets as “bizarre concepts of nutrition and dieting [that] should not be promoted to the public as if they were established scientific principles.”

Meanwhile, these nutritionists would readily admit that they didn’t know what caused obesity (why some people ate too much and others didn’t) and that calorie restriction conspicuously failed to cure it. After nearly twenty years in the field, as Jean Mayer wrote in the introduction to his 1968 monograph,