Body composition by bioelectric impedance and densitometry in black women

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Abstract
Limited body composition data are available on the adult black population, particularly women. This study examined the accuracy of bioelectric impedance analysis (BIA) in predicting hydrostatically measured percentage body fat (% fat) in 98 physically active, eumenorrheic black females. BIA values were also compared to a standard anthropometric method using seven skinfolds. Whole‐body bioresistance (R) was obtained using an RJL Instrument Model BIA‐101. Fat‐free mass (FFM) was predicted from the equation of Lukaski et al. (J. Appl. Physiol. 60:1327–1332, 1986). Body density was measured by hydrostatic weighing (HW) with residual lung volume determined simultaneously. Percent fat was calculated using the Siri (Techniques for Measuring Body Composition, Washington, D.C.: National Academy of Sciences, pp. 223–244, 1961) equation. Compared to HW, BIA significantly underestimated mean FFM (42.8 kg vs. 47.0 kg) and overestimated mean % fat (30.2% vs. 23.4%). Conversely, prediction of % fat and FFM from the sum of seven skinfolds were similar to the criterion values from HW (22.7% vs. 23.4%; 47.4 kg vs. 47.0 kg). Although standard errors of the estimate (SEEs) were similar for BIA (±4.0%) and skinfold (±3.5%) methods, the systematic overestimation of % fat with BIA resulted in only 27 out of 98 black women (28%) having a predicted % fat value within ±4 percentage points of the criterion % fat. In a group of white women (n = 116), % fat values (mean ± SD) were similar between BIA and HW (25.6% ± 6.5 vs. 24.3 ± 5.6). An explanation for this observed racial difference is not readily discernible. Probable variables that may contribute to the higher whole body resistance values for black women include racial differences in skin resistance, body shape and proportions, and relative bone and muscle mass.