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.