An examination of the overlap between genetic and environmental risk factors for intentional weight loss and overeating.

OBJECTIVE To further our understanding of how intentional weight loss (IWL) and overeating are related, we examined the shared genetic and environmental variance between lifetime IWL and overeating. METHOD Interview data were available for 1,976 female twins (both members of 439 and 264 pairs of monozygotic and dizygotic twins, respectively), mean age = 40.61, SD = 4.72. We used lifetime diagnostic data for eating disorders obtained from a semistructured psychiatric telephone interview, examined in a bivariate twin analysis. Both lifetime behaviors were measured on a 3-point scale, where absence of IWL or overeating formed one anchor on the scale and lifetime anorexia nervosa (AN) and bulimia nervosa (BN) formed the opposite anchors, respectively. RESULTS In line with previous findings, a higher body mass index was significantly associated with the lifetime presence of IWL and/or overeating (odds ratio = 1.13, 95% confidence interval (CI): 1.08-1.19). The best fitting twin model contained additive genetic and nonshared environmental influence influencing both IWL and overeating, with correlations between these influences of 0.61 (95% CI: 0.35-0.92) and 0.24 (95% CI: 0.07-0.42), respectively. DISCUSSION About 37% of genetic risk factors were considered to overlap between IWL and overeating, and with only 6% of overlap between environmental risk factors. Thus, considerable independence of risk factors was indicated.