The effect of friends on adolescent body weight.

Using the first wave of the National Longitudinal Study of Adolescent Health (Add Health) survey, this paper examines the influence of peers on adolescent weight. A peer group is defined as a close circle of friends that are identified by a respondent adolescent. After controlling for school fixed effects and for a number of individual, demographic and family characteristics, we find that a higher Body Mass Index (BMI) of close friends is correlated to a higher BMI of the respondent adolescent. However, after instrumental variable analysis is performed, the effect remains significant only among women. We also found that adolescents are more responsive to the body weight of their same gender friends.