Why does a person become overweight or obese? The proximate answer is simple: he consumes more calories than he expends. An answer to the ultimate question, however - why does someone regularly choose to consume more calories than demanded by energy expenditures? - confronts a deep conceptual problem dating back to the Platonic dialogues. How should we regard apparently self-defeating choices, such as gaining unwanted excess weight, where consumption costs and benefits are separate in time, so that today's choices have consequences for one's future "self"?
There are, broadly speaking, two opposing traditions regarding self-defeating choice.3 The first "non-rational" approach regards apparently self-defeating choices as truly self-defeating. Consumers smoke, overindulge in food and drink, pay taxes too soon, and save and exercise too little when they truly would prefer to do otherwise. Agents in the non-rational tradition often do not know or cannot help what they are doing. Their decision making incompetence arises from immaturity, or strong myopia, or irresistible cravings, or systematic decision making errors.
With respect to overeating, the non-rational tradition emphasizes genetic predisposition to excess weight, poor health and nutrition information, or, even with decent information, the systematic inability to make choices consistent with one's preferences.4 These non-rational explanations seem insufficient to us. Obesity does run in families, but genes do not change rapidly enough to account for the last decade's increase in obesity. Similarly, it seems likely that today's heavier consumers are better informed than were their thinner predecessors about the calorie content of foods they eat, and about the health risks of excess weight.5 Nor is it obvious why today's heavier consumers would be more prone to systematic decision errors.
