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.