Estimates of body composition with dual-energy X-ray absorptiometry in adults

Background: Little is known about the distributions of percentage body fat (PBF), total body fat (TBF), and fat-free mass (FFM) in the adult population in the United States. Objectives: We sought to estimate the means and percentile cutoffs of PBF, TBF, and FFM and to assess the differences by sex, age, race-ethnicity, and body mass index in US adults. Design: Data from the National Health and Nutrition Examination Survey (NHANES), which were collected during the 6-y period from 1999 to 2004 and comprise a large nationally representative sample of the US population, were analyzed (n = 6559 men and 6507 nonpregnant women). TBF and FFM were measured by using dual-energy X-ray absorptiometry. PBF was calculated as TBF divided by total mass multiplied by 100. Results: There were large differences between men and women in unadjusted mean PBF (28.1% compared with 40.0%, P < 0.001), TBF (25.4 compared with 30.8 kg, P < 0.001), and FFM (62.3 compared with 44.0 kg, P < 0.001); the sex differences persisted across all body mass index categories after adjustment for age and race-ethnicity (all P < 0.001). The common percentile cutoffs of PBF, TBF, and FFM were estimated by sex, race-ethnicity, and age groups. Equations for the estimation of PBF (R-2 = 0.85), TBF (R-2 = 0.94), and FFM (R-2 = 0.94) according to demographic characteristics and simple anthropometric measures were generated. Conclusion: The estimates of means and percentile cutoffs for PBF, TBF, and FFM, on the basis of NHANES 199922004 dual-energy X-ray absorptiometry data, provide a reference in the US adult population. Am J Clin Nutr 2009;90:1457-65.