It’s tempting to suggest that one reason why the obesity-research community has paid little attention to the logical and scientific deficiencies of the overeating/sedentary-behavior hypothesis is that it becomes difficult even to discuss the subject without constantly tripping over the solecisms it engenders. To say someone “overeats” or “eats a lot” immediately raises the question, Compared with whom? One of the most reproducible findings in obesity research, as I’ve said, is that fat people, on average, eat no more than lean people. They may not eat as little as they say or think they do, but they don’t necessarily eat any more than anyone else. “On the few occasions when the food intake of a group of obese persons has been measured with an approved technique,” wrote the British physiologists J.V.G.A. Durnin and Reginald Passmore in 1967, “it has been found to be no greater than that of a control group of persons of normal weight. Fat people are not necessarily gluttons: some indeed are truly abstemious.” Passmore and Durnin neglected to ask then how such an abstemious individual becomes fat. Rather, they insisted that there was “not a shred of evidence” to support the belief of the obese and “also their friends and sometimes regretfully their medical attendants that they are ‘mysterious engines’ and can conserve energy in an unknown manner.” A mysterious conservation of energy does, however, seem to be the only explanation. Why do they remain fat when others would remain effortlessly lean on the same diet? What does it mean to overeat, if that’s the case?

James Boswell and Samuel Johnson struggled with the same paradox in the late eighteenth century, as Boswell reported in The Life of Samuel Johnson:

Talking of a man who was growing very fat, so as to be incommoded with corpulency; [Johnson] said, “He eats too much, Sir.” Boswell. “I don’t know, Sir; you will see one man fat who eats moderately, and another lean who eats a great deal.” Johnson. “Nay, Sir, whatever may be the quantity that a man eats, it is plain that if he is too fat, he has eaten more than he should have done.”

But to clarify, as Johnson did, that obesity is caused by eating more than one should have, is not a satisfying answer. We’re still left asking why.

This question is built into the logic of the overeating/sedentary-behavior hypothesis. Why do people overeat, or why are they so sedentary, if the inevitable result is obesity? And because both overeating and deficient physical activity are, after all, behavioral conditions, not physiological ones, the only answer allowed by the hypothesis is a judgment on the behavior of the obese. To say that the obese eat more than they should, as Johnson phrased it, or are less active than they should be—thus, inducing their positive caloric balance—implies only two possibilities. Either it’s beyond their control, in which case there is another, more profound cause of their condition—perhaps a metabolic or hormonal disorder for which we should still be searching—or it is within their control, and so we are led to the judgment that the obese are weaker of will than the lean. It may be true, as von Noorden noted, that their appetite is unable to regulate their energy consumption, but why, then, do they not consciously adjust? The logic keeps taking us in circles.