title: Validation of DXA body composition estimates in obese men and women.
abstract: 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.
authors.affiliation: School of Pharmacy and Medical Sciences, University of South Australia, South Australia, Australia. joe.laforgia@unisa.edu.au
authors.forename: Joseph
authors.initials: J
authors.lastname: LaForgia
authors.forename: James
authors.initials: J
authors.lastname: Dollman
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Dale
authors.forename: Robert T
authors.initials: RT
authors.lastname: Withers
authors.forename: Alison M
authors.initials: AM
authors.lastname: Hill
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods*; D000273:Adipose Tissue / Q000503:physiopathology; D000328:Adult; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D001834:Body Water / Q000502:physiology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009765:Obesity / Q000503:physiopathology*; D012044:Regression Analysis