Age at dieting onset, body mass index, and dieting practices. A twin study.

OBJECTIVE

Using a twin study design, we sought to determine whether an early age at dieting onset is a risk factor for higher adult body mass index (BMI) or use of risky dieting practices, independent of genetic and familial factors.

METHOD

Female twins ages 18-60 years (N=950) from the University of Washington Twin Registry completed 2 surveys an average of 3 years apart. Analyses of individual twins and within-twin pairs tested associations of self-reported age at dieting onset with (1) adult BMI at baseline, (2) change in BMI between the two surveys and (3) risky dieting behaviors at baseline.

RESULTS

In analyses mimicking studies of unrelated individuals, an earlier age at dieting onset was associated with greater adult BMI (p=0.003), higher Restraint Scale scores (p<0.001), greater use of risky dieting behaviors (p=0.04) and more weight cycling episodes (p<0.001). In within-pair models that control for genetic and familial factors, the only significant association was between an earlier age at dieting onset and more weight cycling episodes (p=0.006).

DISCUSSION

Underlying genetic and familial factors may influence associations of early dieting with higher adult BMIs and risky dieting practices in women.