Why are Educated Adults Slim — Causation or Selection?

More educated adults tend to have lower body mass index (BMI) and a lower risk of overweight and obesity. We contrast two explanations for this education gradient in BMI. One explanation is selection: adolescents who have lower BMI are more likely to plan for, attend, and complete higher levels of education. An alternative explanation is causation: higher education confers lifelong social, economic, and psychological benefits that help adults to restrain BMI growth. We test the relative importance of selection and causation using data from the National Longitudinal Survey of Youth, 1997 cohort (NLSY97), which tracks BMI from adolescence (age 15) through young adulthood (age 29). Ordinal regression models confirm that lower-BMI adolescents do select into higher education. Fixed-effects models suggest that the causal effect of education on BMI is significant but accounts for only one-quarter of the mean BMI differences between more and less educated adults at age 29. Among young adults, it appears that most of the education gradient in BMI is due to selection.