Separating Social and Biological Processes: Relative Versus Absolute Body Weight and Youth Outcomes

A large literature has shown that people, especially women, with higher body mass index (BMI) face a range of negative life outcomes, including lower human capital accumulation and worse mental health. While both biological and sociological theories would suggest these relationships, social scientists interested in uncovering the social effects of BMI have been forced to use absolute (i.e., biological) rather than relative (i.e., social) BMI in their analyses. However, absolute measures of body mass conflate biological and social effects, and more importantly, fail to operationalize sociological theories. This, in turn, leads to mixed evidence on the links between BMI and adolescent outcomes as well as a lack of understanding of the social effects of BMI. This study uses data from the National Longitudinal Study of Adolescent to Adult Health (Add Health), leverages a quasi-experimental research design, and utilizes a relative measure of body mass. Results show that women with high relative BMI in U.S. high schools face substantial mental health burdens that translate into higher levels of school dropout, even after adjusting for absolute BMI. A component of these effects is from higher odds of social marginalization among women with relatively high BMI. Based on these results, this study argues that it is essential to operationalize sociological theories, in part by shifting away from the empirical focus on absolute BMI in the literature, to make further progress in understanding how BMI affects life outcomes.