Reliability of body-fat estimations from a four-compartment model by using density, body water, and bone mineral measurements.

Reliability of body-fat estimation by a four-compartment model was tested in 10 subjects. Body densities were measured by underwater weighing (UWW), total body water (TBW) by deuterium dilution, and total body bone mass (TBBM) by dual-energy x-ray absorptiometry in three sessions in 1 wk. Percent body fat was determined by [2.559/density -0.734 (TBW/weight) +0.983 (TBBM/weight) -1.841] x 100. Reliability coefficients were 0.991 and 0.994, and within-subjects standard deviations were +/- 1.0 and +/- 1.1 for percent body-fat estimations from Siri's two-compartment and the four-compartment models, respectively; fat mass was +/- 0.8 kg with both models. These data suggest that additive errors in the multicompartment model do not offset the improved accuracy of fat estimations over those obtained from UWW alone. The greatest source of error came from UWW procedure itself (+/- 0.002 g/cm3, or approximately 1.0% of body weight), followed by error in TBW (+/- 0.5 L). More reproducible passive methods that are not dependent on hydration or TBBM may be especially useful after validation against the four-compartment model.