In order to explain the differences in obesity rates among women in the United States by education, we model a social process in which body weight norms are determined endogenously in relation to the weight distribution of the peer group. The model features biologically grounded variation in metabolism, and enables us to describe a complete distribution of weights in equilibrium. We assume that individuals compare themselves to others with the same level of education, and that the importance of conforming to the group weight norm increases with education status. Consistent with observed body weights among women in the United States, the model predicts lower average weights and less dispersion of weight among more educated women.