Undue influence of weight on self-evaluation: A population-based twin study of gender differences

Objective: To explore the extent to which genetic and environmental factors contribute to liability to placing undue importance on weight as an indicator of self-evaluation and to determine whether differences exist across genders in the nature and magnitude of these effects. Method: Self-report data were collected on 8,045 same-sex and opposite-sex twins, aged 18-31, years, from a population-based registry of Norwegian twins. Structural equation modeling was utilized to estimate the relative contribution of genetic and environmental factors to liability for undue influence of weight on self-evaluation, allowing for gender-specific effects. Results: Individual variation in undue influence of weight on self-evaluation was best explained by shared and individual environmental influences. No significant gender differences were found. Shared environmental factors accounted for 31% of the variance. Discussion: These results raise the possibility that there may be distinct sources of familial resemblance for different symptoms of bulimia nervosa as codified in the 4th ed. of the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1994). (C) 2004 by Wiley Periodicals, Inc.