Peer Effects, Fast Food Consumption and Adolescent Weight Gain *

This paper aims at opening the black box of peer effects in adolescent weight gain. Using Add Health data on secondary schools in the U.S., we investigate whether these effects partly flow through the eating habits channel. Adolescents are assumed to interact through a friendship social network. We first propose a social interaction model of fast food consumption. Our approach allows to control for correlated effects at the network level and to solve the simultaneity (reflection) problem. We exploit results by Bramoullé, Djebbari and Fortin (2009) which show that if there are two agents who are separated by a link of distance 3 within a network (i.e., two adolescents who are not friends but are linked by two friends), peer effects are identified. The model is estimated using maximum likelihood and generalized 2SLS strategies. We also estimate a panel dynamic weight gain production function relating an adolescent's Body Mass Index (BMI) to his current fast food consumption and his lagged BMI level. Results show that there are positive significant peer effects in fast food consumption among adolescents belonging to a same friendship school network. The estimated social multiplier is 1.59. Our results also suggest that, at the network level, an extra day of weekly fast food restaurant visits increases BMI by 2.4%, when peer effects are taken into account. Lee for useful discussions. All remaining errors are ours. Financial support from the Canada Research Chair in the Economics of Social Policies and Human Resources and le Centre interuniversitaire sur le risque, les politiqueséconomiques et l'emploi is gratefully acknowledged. Hill, and funded by grant P01-HD31921 from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, with cooperative funding from 23 other federal agencies and foundations.