The terms “overeating” and “deficient physical exercise” are applied only to the overweight and obese. “If eating behavior did not produce deposits of body fat we could not call it overeating,” is how this phenomenon was phrased in 1986 by William Bennett, then editor of the Harvard Medical School Health Letter and one of the rare investigators interested in obesity ever to make this point publicly. If someone is fat, then he has overeaten by definition. If he’s lean, the amount of food he consumes is not considered relevant to his weight, nor is the amount of physical activity in his life. This is why lean individuals who consume comparatively large quantities of food are said to have a healthy appetite or are big eaters. No one suggests that they are suffering from excess calorie consumption.

Von Noorden’s proposition, which still obtains today, is the equivalent of saying that “alcoholism is caused by chronic overdrinking” or “chronic fatigue syndrome is caused by excessive lethargy and/or deficient energy.” These propositions are true, but meaningless. And they confuse an association with cause and effect. They tell us nothing about why one person becomes obese (or alcoholic or chronically fatigued) and another person doesn’t. Moreover, as Bennett noted, even if fat people did eat more and/or expend less energy than most or all lean people—something that has never been shown to be true—it would still beg what should be the salient question in all obesity research: why wasn’t intake adjusted downward to match expenditure, or vice versa? Nor does it explain why reversing this caloric imbalance fails to reverse the weight gain reliably.*83

Those who are overweight or obese, with exceedingly rare exceptions, do not continue to gain weight year in and year out. Rather, they gain weight over long periods of time and then stabilize at a weight that is higher than ideal, remaining there for a long period of time, if not indefinitely. Why, as Bennett asked, “is energy balance achieved at a particular level of fat storage and not some other?” This is another question that any reasonable hypothesis of obesity must address. In 1940, the Northwestern University endocrinologist Hugo Rony described the problem in a way that brings to mind Hirsch’s comment of fifty years later: “An obese person who maintains his weight at 300 pounds indefinitely, is in caloric equilibrium the same as any person of normal weight. The conception that his obesity is due to positive caloric balance might be useful in explaining how he reached this excessive weight, but cannot inform us why he maintains it, why he resists attempts to reduce it to normal, why he tends to regain it after successful reduction.”