Gender-assortative weight gain: reply to Leary, Smith and Ness

Abstract

In the July 2009 issue of IJO, the EarlyBird study1 reported a strong gender-assortative relationship such that, at the age of 8 years, the daughters (but not the sons) of obese mothers were some 10-fold more likely to be obese than those of normal-weight mothers, and the sons (but not the daughters) of obese fathers some sixfold more likely. The phenomenon was dynamic (it strengthened over time), and the effect size of the gender interaction at ~1.2 is perhaps the largest reported in childhood obesity. Indeed, the offspring of same-sex normal-weight parents were no heavier than the standards of 1990 based on children born 30 years ago. The findings suggest that contemporary childhood obesity is largely confined to the offspring of obese same-sex parents and it sits comfortably with the observation that, although the mean body mass index (BMI) of pre-pubertal children has risen substantially in a generation, the median has barely changed.