Bio-impedance analysis for estimation of total body potassium, total body water, and fat-free mass in white, black, and Asian adults.

Bio-impedance analysis (BIA) measurements have been used to predict components of body composition. Their validation is required for populations varying in race, sex, and age. In 371 Whites, 182 Blacks and 225 Asians, single-frequency BIA at 50 kHz (RJL-100) resistance and reactance measurements were correlated with same-day measurements of total body water (TBW) by THO dilution, total body potassium (TBK) by whole body K counting, and fat-free mass (FFM) by dual-photon absorptiometry.

Body fat by dual photon absorptiometry: Comparisons with traditional methods in Asians, blacks, and whites.

Measurement of body fat by dual photon absorptiometry (Fat ) is based on the physical principles of differential attenuation of discrete photons by fat and other soft tissue components. The three traditional methods of measuring fat are indirect, in that they depend on measuring the fat free mass (FFM) based on the assumed constancy of water, potassium, and density in the FFM. Comparison of Fat with fat measured by each of the indirect methods discloses systematic differences which shed light on the nature of the constancy assumptions.