1 Obesity and the Consumption Underestimation Bias

3 We contend that people’s perception of the number of calories in a meal follows a compressive psychophysical power function and therefore becomes less sensitive as the number of calories of the meal increases. We show, mathematically and empirically, that this psychophysical model solves two enigmatic cross-disciplinary findings: (1) why people systematically underestimate their consumption and (2) why this consumption underestimation bias is more pronounced for overweight people. Five experiments show strong support for the hypothesized model across pre-and post-intake estimations, chosen and nonchosen meals, single and repeated estimations, and separate and joint estimations. We also find that the psychophysical relationship between the estimated and actual number of calories of a meal is independent of the respondent’s carelessness, debiasing knowledge, impression management, or estimation anchor—four explanations that have been invoked to explain consumption estimation biases. Our finding that calorie underestimation is caused by meal size and not body size leads to innovative strategies to improve consumption quantity estimations