Ludwig and Ebbeling1 compare 2 mechanistic models of obesity, the so-called conventional model (CM) and the carbohydrate-insulin model (CIM). The CM considers energy intake and expenditure to be functionally independent processes receiving no feedback from circulating fuels or endocrine signals. Food intake and physical activity are portrayed to be under conscious control, albeit subject to environmental influences. Thus, preventing and treating obesity simply requires the willpower to eat less and move more.