Validation of DXA body composition estimates in obese men and women

The aim of this study was to determine the accuracy of dual-energy X-ray absorptiometry (DXA)-derived percentage fat estimates in obese adults by using four-compartment (4C) values as criterion measures. Differences between methods were also investigated in relation to the influence of fat-free mass (FFM) hydration and various anthropometric measurements. Six women and eight men (age 22-54 years, BMI 28.7-39.9 kg/m 2, 4C percent body fat (%BF) 31.3-52.6%) had relative body fat (%BF) determined via DXA and a 4C method that incorporated measures of body density (BD), total body water (TBW), and bone mineral mass (BMM) via underwater weighing, deuterium dilution, and DXA, respectively. Anthropometric measurements were also undertaken: height, waist and gluteal girth, and anterior-posterior (A-P) chest depth. Values for both methods were significantly correlated (r 2 = 0.894) and no significant difference (P = 0.57) was detected between the means (DXA = 41.1%BF, 4C = 41.5%BF). The slope and intercept for the regression line were not significantly different (P > 0.05) from 1 and 0, respectively. Although both methods were significantly correlated, intraindividual differences between the methods were sizable (4C-DXA, range = 3.04 to 4.01%BF) and significantly correlated with tissue thickness (chest depth) or most surrogates of tissue thickness (body mass, BMI, waist girth) but not FFM hydration and gluteal girth. DXA provided cross-sectional %BF data for obese adults without bias. However, individual data are associated with large prediction errors (±4.2%BF). This error appears to be associated with tissue thickness indicating that the DXA device used may not be able to accurately account for beam hardening in obese cohorts.