This article explores the relationship between time preferences, economic incentives and body mass index (BMI). We provide evidence of an interaction effect between time preference and food prices, with cheaper food leading to the largest weight gains among those exhibiting the most impatience. The interaction of changing economic incentives with heterogeneous discounting may help explain why increases in BMI have been concentrated amongst the distribution's right tail. We also model time-inconsistent preferences by computing individuals’ quasi-hyperbolic discounting parameters. Both long-run patience and present-bias predict BMI, suggesting obesity is partly attributable to both rational intertemporal tradeoffs and time inconsistency.