Journal of the European Economic Association
Exercise or Extra Fries? Behavioral Drivers of Obesity Over the Life Cycle,
2026-09-05
As America faces an obesity epidemic and its economic consequences, the factors driving weight variation across the U.S. population remain unclear, especially since these differences extend well beyond commonly studied channels like income or education. We leverage a unique thirty-year panel of U.S. registered nurses to examine the changes in body mass index (BMI) with age, the impact of lifestyle choices on body weight in adulthood, and the role of inherited metabolic traits and childhood preference formation. Our empirical findings reveal that among individuals who enter adulthood with a healthy body mass, those in the top diet quality or exercise deciles at age thirty are roughly 50% more likely to maintain a healthy BMI and avoid morbidities three decades later, compared to those in the bottom deciles. To better understand the drivers of weight gain, we propose a novel structural framework of endogenous BMI evolution where initial heterogeneity is amplified by behaviors to explain much of the observed divergence in weight. Counterfactual experiments using the model indicate that initial conditions, such as fixed metabolic types, account for at least one-third of the variance in weight at older ages. While course correction through behaviors can only partially compensate for poor initial conditions at the onset of adulthood, we find that promoting healthy behaviors in adults can reduce total health care expenses by at least 8% annually.