This paper analyzes the importance of social ties for eating behavior of US youth.
We propose a novel approach that addresses identi…cation of social endogenous
e¤ects. We overcome the problem of measuring the separate impact of endogenous
and contextual e¤ects on individual Body Mass Index (BMI) in a dynamic linear-
in-means model, where individual- and group-speci…c unobservable e¤ects are
controlled for. We show that the main drivers of eating behavior are habituation and
imitation e¤ects. Imitation e¤ects explain most of the variation in BMI of individuals
who were normal-weight and overweight during adolescence. Obese adolescents,
instead, become future obese adults through wrong habits enforced by imitative
behavior.