In 1961, William Leith of McGill University reported his clinical experience with forty-eight patients on Pennington’s diet all of whom had previously tried low-calorie diets “without measurable success.” Half had used appetite-suppressant drugs (“anorectic agents,” as Leith called them), seven had taken “bulk substitutes,” and “eight had participated in group psychotherapy for a period of eight months,” and yet “none of them showed a sustained loss of weight.” Twenty-eight, by contrast, lost a significant portion of their excess weight on Pennington’s diet—between ten and forty pounds, averaging one and a half pounds each week. “Our results do show that satisfactory weight loss may be accomplished by a full caloric, low carbohydrate diet,” Leith concluded. “The patients ingested protein and fat as desired.” For the successful dieters, a significant success had followed a lifetime of failure.

Neither the individuals who wish to lose weight nor the clinicians who prescribe the diet need a randomized trial to tell them if it works. Such a trial is necessary only to establish that the diet works better than some other diet, and whether it leads to sustained benefits in health and longevity.

Until recently, few nutritionists or clinicians considered it worth their time and effort to test weight-reducing diets. Instead, they spent their careers studying the physiological and psychological abnormalities associated with the condition of obesity, comparing food consumption and physical activity in obese and lean individuals, and studying obesity in animals. They tried to induce fat people to endure semi-starvation by behavioral modification; they studied pharmacological methods of suppressing hunger, or surgical methods of reducing the amount of food that could be consumed or digested.*101 Testing diets or even treating obese patients was regarded as lesser work. “To be honest, obesity treatment is extremely boring,” said Per Björntorp, who was among the most prominent European authorities on obesity in the 1970s and 1980s. “It’s very difficult and unrewarding.” When obese individuals came to his biochemistry laboratory at the University of Göteborg, they were referred to the local nutritionists to be taught how to count and restrict calories. Since everyone knew that obesity was caused by overeating, why bother with diet trials? “There’s no point wasting your time on them,” George Bray, considered one of the world’s leading authorities, said in a recent interview. “If you get restriction of energy you will lose weight, unequivocally. It’s not an issue.”

When clinical investigators did test the efficacy of high-fat, carbohydrate-restricted diets, however, the results were remarkably consistent. Every investigator reported weight losses of between one and five pounds a week even when the investigators running the trial seemed more concerned with establishing that the diets caused deleterious side effects. Every investigator who discussed the subjective experiences of the test subjects reported that they suffered none of the symptoms of semi-starvation or food deprivation—“excessive fatigue, irritability, mental depression and extreme hunger,” as Margaret Ohlson described them.