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Document Type

Article

Abstract

The estimation of body fatness by the densitometric method assumes a constant density of the fat-free body. Water constitutes the largest single component of the fat-free body and because of its relatively low density (.9934 gm/cc at 37°C) exerts the greatest influence on the density of the fat-free body. The purpose of this study was to test the assumption that the water content of the fat-free body (% water- FFB) is constant during growth and development. The sample consisted of 292 Black and White males and females (ages 8-30 years) and was classified via maturational assessment as prepubertal, (N = 54), pubertal (N = 50), postpubertal (N =107) and adult (N = 81). Body water was measured by deuterium oxide dilution and body density was measured by the underwater weighing method. Body water as a percentage of body weight (% water-BW) was higher ( p < .01) for males (X = 61.6%) than females (X = 55.8%) with the greatest difference observed in the pubertal, postpubertal and adult levels. This finding likely reflected the increased relative fatness of females at puberty and is in agreement with skinfold thickness measurements. The % water-FFB progressively decreased from prepubescence to adulthood by 2.8% overall at a rate of 0.38% per year for both sexes with the lowest values found in the adult samples. Although the % water-FFB of the prepubertal and pubertal groups was similar (p > .05), both groups were significantly (p < .01) higher than the postpubertal and adult groups, and the postpubertal group was higher (p < .05) than the adult group. Moreover, the % water-FFB was lower (p < .05) for males (X = 73.5%) than females (X = 74.2%).No difference in % water-FFB was found between the Black and White samples. These findings suggest that the water content of the FFB is not constant during growth and development and that adult equations for estimating fat from density and other indirect methods may not be appropriate for children, overestimating fatness by at least 4%.

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