Background. The study explored the genetic and environmental risk factors for both the behaviours and attitudes characteristic of disordered eating.

Methods. In three waves of data collection, information was collected from female twins regarding their eating and attitudes towards eating, weight and shape. The first assessment consisted of a self-report questionnaire (1988–9) with 1682 women. The second assessment consisted of a semi-structured psychiatric interview schedule (1992–3), completed by 1852 women, many of whom had completed Wave 1 assessment. The third assessment, with 325 women chosen from Waves 1 and 2 (1995–6), consisted of a semi-structured interview (the Eating Disorder Examination).

Results. As only one twin pair was concordant for lifetime bulimia nervosa at Wave 3 assessment, ordinal measures of all assessments were used in a multivariate genetic analysis. Results indicated that additive genetic and non-shared environmental influences best explained variance in liability to disordered eating, with about 60% (95% CI 50–68) of the variance explained by genetic factors. Comparison with a model allowing for the effects of shared environment indicated genetic factors accounted for a similar degree of variance (59%, 95% CI 36–68).

Conclusion. Liability to the development of the behaviours and attitudes characteristic of eating disorders is best explained by both environmental and genetic factors, with covariation between the three measures best explained by a single latent phenotype of disordered eating which has a heritability of 60%.