Genetic influences on disordered eating behaviour are largely independent of body mass index.

OBJECTIVE Prior studies suggest eating disorders and related characteristics are moderately to substantially heritable. We are interested in identifying the genes underlying disordered eating behaviour (DEB), and want to know how much of the genetic influence underlying DEB is attributable to genetic influences on body mass index (BMI). METHOD Bivariate analyses were performed, in adolescent twins and siblings, to estimate the genetic and environmental contributions for DEB, BMI, and their overlap. RESULTS Shared genetic risk factors explained the overlap between BMI and DEB (genetic correlation was 0.43 in women, 0.51 in men). DEB was highly heritable in women (a(2) = 0.65; a(2) independent of BMI = 0.53) and moderately heritable in men (a(2) = 0.39; a(2) independent of BMI = 0.29). BMI was highly heritable in both men (a(2) = 0.76) and women (a(2) = 0.80). CONCLUSION The entire correlation between DEB and BMI was explained by shared genetic risk, but the majority of genetic influences on DEB were due to genetic effects independent of BMI.