In Vivo Neutron Activation Analysis for Body Fat: Comparisons by Seven Methods

Abstract

All current well-accepted traditional methods for measuring body fat are indirect, in that they measure fat-free mass (FFM) based on the assumed constancy of water, potassium, or density in the FFM^7–3. Newer methods such as bio electrical impedance analysis (BIA) are calibrated by traditional indirect methods. Dual-photon absorptiometry (DPA) is the most promising and relatively available new method^4,5 which bypasses the traditional assumptions of chemical constancy, in that it avoids the errors due to the assumptions underlying each of the traditional methods. However, recent studies indicate that the currently used DPA system is not yet well calibrated for measuring fat content in soft tissue areas with thickness less than 10 cm or greater than 30 cm. In vivo neutron activation analysis (IVNA) measures the FFM by the direct measurement of each of the chemical elements in the FFM⁶, and thus sets a better standard for measuring body composition in vivo. The purposes of this report were 1) to make comparisons between IVNA and seven currently widely used methods for estimating body fat, and 2) to develop models for predicting IVNA-measured body fat by these seven indirect methods in whites and blacks.