If we can believe that people become obese because they simply ignored the fact that they were getting increasingly fatter, year in and year out, with the passive accumulation of excess calories, and that by the time they noticed it was either too late to do anything about it or they really didn’t care (despite claims they might make to the contrary); if we can believe that obese individuals fail to survive indefinitely on semi-starvation diets because they are gluttonously unwilling to forgo temptation and so prefer, consciously or unconsciously, obesity to a life of moderation, then, as Stunkard observed in 1959, the matter is settled. Our job is done. But, of course, it isn’t.

The more thoughtful analyses of obesity over the years have inevitably taken a more empathic view of those who suffer from it. They posit that there is no scientifically justifiable reason—or evidence—to assume that the obese are any more defective in character or behavior than you or I. Eric Ravussin, a diabetologist and metabolism researcher who began studying obesity among the Pima in 1984, has reported that Pima men who gained excessive weight—more than twenty pounds—over the course of a three-year study had a significantly lower basal-metabolic rate before their weight gain than men who remained relatively lean. (This same observation, as Ravussin points out, was made in infants: those who are heavier at one year of life have abnormally low daily energy expenditures when they are three months old.)*85 This suggests a constitutional difference in these individuals; it would be difficult to explain it in terms of sloth and a weak character. As a result, Ravussin questioned the logic and implications of the positive-caloric-balance hypothesis. “If obesity was only caused by an excessive appeal for food,” Ravussin asked in a 1993 article in the journal Diabetes Care, “how can we explain the complete failure of treating it with behavioral therapies? Can we really believe that so many obese patients are liars and are cheating their doctors? How many more times do we need to demonstrate the high rate of recidivism among obese patients after weight loss to persuade others that unwanted metabolic forces contribute significantly to the causes of obesity in man?”

When Ravussin was interviewed more recently, he insisted that overeating and sedentary behavior could not explain the prevalence of obesity and diabetes in modern societies, and particularly not in the Pima. “I was shocked when I went to work with the Pima and I saw the amount of suffering in this population,” he said. “It’s not fun to see your mother [having a limb] amputated when she’s thirty-two or thirty-five because she’s had poorly controlled diabetes for twenty years. There’s not a population in the world as aware as the Pima of the damages of diabetes and obesity. They know that. They are told from the age of two to avoid it, and still they cannot make it.”