Differences in the subcomponents of fat-free body in relation to height between black and white children

The individual subcomponents of fat-free body (FFB) in relation to height were investigated in 131 white (N = 85) and black (N = 46) males (MW, MB) and 108 white (N = 63) and black (N = 45) females (FW, FB), aged 8 to 18 years. Bone mineral content (BM), bone width (BW), and bone mineral index (BMI) were measured using photon absorptiometry; total body water (TBW) was measured by deuterium dilution; body density was measured by hydrostatic weighing, correcting for residual lung volume; and estimates of lean body mass (LBM) were made from total body potassium (⁴⁰ K spectroscopy). The subcomponents of the FFB-BM, BW, BMI, TBW, and K-were regressed on the log of height to determine the exponent of the independent variable (Ht) that would most accurately predict the dependent variables (BM, BW, BMI, TBW, K) within gender and race. Regression equations were derived for each of the variables used to represent a subcomponent of the FFB on Ht. Significant (P < .05) racial differences were found in BW, with the MB having wider bones than the MW. Significant racial differences were observed in BMI with FB demonstrating a greater difference across height than FW. Racial differences in BM and TBW approached significance within the female sample. At heights greater than the mean of a typical pubescent child, the males had higher values for each of the variables, except for BMI, than did the females. The lower BMI values observed in males indicated that the rate at which male bones grow in width was greater than their rate of mineralization. Within the male sample, blacks had higher bone mineral than whites with the magnitude of these differences dependent on the variable under consideration. Within the female sample the blacks had greater amounts of BM and BMI in relation to height, while the whites had a greater amount of K. Therefore, the magnitude of the differences between blacks and whites in the subcomponents of the FFB are dependent on gender, stature, and the particular subcomponent of the FFB under consideration.