Genetic and environmental correlations between obesity and body fat distribution in adult male twins.

Genetic and environmental correlations between measures of obesity [body mass index (BMI)] and body fat distribution [waist/hip ratio (WHR) and subscapular/triceps ratio (SSTR)] were examined in 133 monozygotic and 129 dizygotic pairs of elderly white male twins, age 59 to 70 years, participating in the third cardiovascular examination of the National Heart, Lung, and Blood Institute Twin Study. The BMI, WHR, and SSTR fat measures were significantly correlated in these twins, with BMI more closely related to WHR (r = 0.52) than to SSTR (r = 0.18), and the WHR-SSTR association intermediate (r = 0.27). Multivariate genetic analyses of the three indexes using the LISREL modeling approach indicated a significant heritable component for each fatness variable, h2 = 0.66, 0.46, and 0.25 for BMI, WHR, and SSTR, respectively, and a significant correlation between genetic influences on BMI and WHR (genetic r = 0.51). The common genetic component accounted for 54% of the observed BMI-WHR correlation, suggesting that overall obesity and abdominal adiposity distribution are mediated to some extent by similar genetic influences. The genetic correlations between SSTR and BMI and between SSTR and WHR were not significantly different from zero, suggesting that genetic influences on skinfold distribution are independent of those on abdominal body fat and overall obesity. The genetic findings support the hypothesis that the WHR and SSTR indexes do not assess the same dimensions of fat patterning.