The sumo wrestlers of Japan, whose weight commonly exceeds three hundred pounds, typically reach that level by their early twenties. In 1976, a University of Tokyo collaboration, led by Tsuneo Nishizawa, published an article in The American Journal of Clinical Nutrition that still constitutes the most comprehensive analysis in the English medical literature of the sumo diet, body composition, and health. The world of professional sumo wrestling, according to Nishizawa, is divided into an “upper group,” constituting the best wrestlers in the country, and a “lower group.” The members of the upper group consumed on average some fifty-five hundred calories’ worth of chanko nabe (a pork stew) a day, out of which 780 grams were carbohydrates, 100 grams fat and 365 grams protein. This constituted more than twice the calories and carbohydrates of the typical Japanese diet of the era,*90 slightly less than twice the fat, and four and a half times the amount of protein. The sumo diet was very high in carbohydrate by our standards—57 percent of the calories—and very low in fat—16 percent—considerably beneath what most public-health authorities in America consider a feasible low-fat target. The lower group of sumo weighed as much as their more accomplished colleagues, but were significantly fatter and less muscular. They consumed, on average, only 5,120 calories of chanko nabe a day, consisting of 1,000 grams of carbohydrates, 165 grams of protein, and only 50 grams of fat; these lesser sumo attained and maintained their corpulence on a diet of nearly 80 percent carbohydrate calories and 9 percent fat.

It seems that if we wanted to design a diet capable of inducing pathological obesity in young men in their prime, we might start with just such a very low-fat, high-carbohydrate diet. The diet would provide an enormous amount of calories, which might be the salient factor, but we would have to wonder what it is about this dietary composition that allows for such extraordinary overconsumption, not just for a few days, but for years or perhaps decades.

For the past quarter century, public-health authorities and obesity researchers have insisted that it is dietary fat, not carbohydrates, that fattens most effectively and causes obesity. This is why low-fat, low-calorie diets are recommended for weight loss as well as prevention of heart disease. This notion is based on four pieces of evidence, all of which are easily challenged.

The one that has been most influential is the association between heart disease, obesity, and diabetes. If heart disease is caused by high-fat diets, as is commonly believed, then so are obesity and diabetes, since these diseases appear together in both individuals and populations. But there is no evidence linking obesity to dietary-fat consumption, neither between populations nor in the same populations.*91 And, of course, if dietary fat is not responsible for heart disease, then it’s unlikely that it plays a role in obesity and diabetes.