The association of restrained eating with weight change over time in a community-based sample of twins

We investigated the association of restrained eating with BMI and weight gain while controlling for the influence of genes and shared environment. Participants were 1,587 twins enrolled in the University of Washington Twin Registry (UWTR). Restrained eating was assessed by the Herman and Polivy Restraint Scale. Height and weight were self-reported on two occasions. Analyses used generalized estimating equations or multiple linear regression techniques. Restraint Scale scores were positively associated with both BMI (adjusted beta = 0.39 kg/m(2); 95% confidence interval (CI) = 0.34-0.44; P < 0.001) and weight gain (adjusted beta = 0.33 pounds; 95% CI = 0.17-0.49; P < 0.001). High Restraint Scale scorers had an adjusted mean BMI of 27.9 kg/m(2) (95% CI = 27.4-28.4) as compared to intermediate (mean = 25.5 kg/m(2); 95% CI = 25.2-25.8) and low scorers (mean = 23.0 kg/m(2); 95% CI = 22.7-23.3). In within-pair analyses among 598 same-sex twin pairs, the adjusted association between Restraint Scale scores and BMI persisted even when genetic and shared environmental factors were controlled for (adjusted beta = 0.18; 95% CI = 0.12-0.24; P < 0.001), as did the association with weight gain (adjusted beta = 0.37; 95% CI = 0.13-0.61; P = 0.003). In stratified analyses, dizygotic (DZ) twins differed more in BMI for a given difference in the Restraint Scale score than monozygotic (MZ) twins, for whom genetics are 100% controlled (adjusted beta = 0.32; 95% CI = 0.20-0.44 vs. adjusted beta = 0.10; 95% CI = 0.04-0.16; P = 0.001 for test of interaction). These data demonstrate that observed relationships between BMI, weight gain, and restrained eating, as assessed by the Restraint Scale, have a strong environmental influence and are not solely due to shared genetic factors.