Fat-Free Mass and Percent Body Fat Assessments by Dual-Energy X-ray Absorptiometry, Densitometry and Total Body Water
In recent years, noninvasive measurements for determining body composition have included dual-energy projection methods, which provide skeletal as well as soft tissue measurements for total and regional body composition1. The use of dual photon absorptiometry for body composition measurements is based upon the differential attenuation by tissue of photons from two different energy levels emerging from an X-ray source or from a radionuclide. The acronym DXA will be adopted for dual-energy X-ray absorptiometry throughout this text in accordance with the recommendations of Wilson et al.2. Dual-energy projection methods are independent of assumptions about biological constancies of tissue densities that characterize traditional methods such as hydrometry and the two-component densitometric model. These are based on the main assumption that the density of fat-free mass is constant. However, the density of fat-free mass varies depending on the amounts of water, protein and mineral present and according to ethnicity, gender, age and determinants of fatness such as exercise and illnesses3. For clinical and research purposes, it is important to compare results from methods developed recently such as DXA with body composition techniques that have a longstanding tradition. The purpose of this study is to compare fat-free mass (FFM) and percent body fat (%BF) as obtained by dual-energy X-ray absorptiometry (DXA), densitometry (DENS) and deuterium dilution for total body water (TBW).
KeywordsHydration Attenuation Radionuclide Triglyceride Deuterium
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