Hruschka et al. Respond

Abstract

We thank Dr. Bartle for pointing out that clustering of obesity in families would be expected given shared genetics. Of course, we would also expect that common home environment plays a role.1 Our key finding that shared social norms only weakly account for shared body size in a sample including both family and friends leaves room for developing a number of plausible alternative hypotheses for the social bases of obesity clustering, including some that more directly take into account genetics. But as obesity has demonstrated high heritability and a large norm of reaction, we would expect that the most ultimately satisfying answers must be focused on interactions between relevant genetic pathways and the physical and social environment. We are especially encouraged in this regard by recent findings on the developmental origins of obesity,2 interactions between feeding environment and genetic risk,3 and genetic influences on how people construct their social environments.4 A direct focus on mechanisms—whether by examining how body size ideals influence behavior or by mapping specific genetic pathways—will be the crucial step in understanding how and why the social environment matters to the obesity epidemic.