Environmental influences on young adult weight gain: evidence from a natural experiment.

OBJECTIVES This study investigated the importance of environmental influences in explaining weight gain and related behaviors among freshman college students. METHODS We exploited a natural experiment that takes place on most college campuses in the United States--randomized dormitory assignments. We estimated the effects of living in dormitories with varying physical environment characteristics on weight gain and related behaviors (daily number of meals and snacks, weekly frequency of exercise) among randomly assigned freshman students. RESULTS We found strong evidence linking weight and related behaviors to individual dormitories, as well as to specific characteristics of the dormitories. On average, students assigned to dormitories with on-site dining halls gained more weight and exhibited more behaviors consistent with weight gain during the freshman year as compared with students not assigned to such dormitories. Females in such dormitories weighed .85 kg (p = .03) more and exercised 1.43 (p < .01) times fewer; males consumed .22 (p = .02) more meals and .38 (p = .01) more snacks. For female students, closer proximity of the dormitory to a campus gym led to more frequent exercise (.54, p = .03), whereas living closer to central campus reduced exercise (-.97, p = .01). CONCLUSIONS Using a natural experiment to deal with the potential endogeneity of the living environment, this study found that the physical environment affects both students' weight changes and weight-related behaviors.