Potassium Content of the Fat-Free Body: Effects of Gender, Race, Maturation, and Age

Variability associated with the effects of gender, race, maturation (ML), and age on the potassium content of the fat-free body (K/FFB) was investigated in 163 males and 112 females ages 8 to 30 years. Measures of body density (hydrostatic weighing), bone mineral content (single photon absorptiometry), total body water (modified deuterium dilution), and whole body potassium (⁴⁰K spectroscopy) were obtained. FFB was calculated using a multicomponent equation which accounted for the variability in FFB mineral and water content. Subjects were classified by maturation as prepubescent, pubescent, postpubescent, and adult (Tanner stages). Least-squares multiple regression analysis revealed significant (p<.05) effects of gender and maturation as well as an interaction between whites and blacks with maturation. The significant increase in K/FFB across maturation and age was most evident in the male sample for both racial groups, with K/FFB increasing from 2.37 in prepubescents to 2.54 in adults. The magnitude of increase in K/FFB across maturation was smaller and not statistically significant within the female sample. Hence, consideration of gender, maturation, and age is important in estimating FFB from total body potassium.