Body-composition changes with diet and exercise in obese women: a comparison of estimates from clinical methods and a 4-component model

Background: Most methods available to clinicians for estimating body-compos ition changes have been validated against estimates from densitometry, base d on a 2-component (fat mass and fat-free mass) model. Objective: Estimates of changes in percentage body fat (%BF) from dual-ener gy X-ray absorptiometry (DXA), skinfold thicknesses (SFTs), bioelectrical i mpedance analysis (BIA), and body mass index (BMI; in kg/m(2)) were compare d with estimates from a 4-component (fat, water, mineral, and protein) mode l (%BFd,w,m), a more accurate method. Design: Determinations of body density from hydrostatic weighing, body wate r from deuterium dilution, bone mineral and %BF from whole-body DXA, resist ance from BIA, and anthropometric measures were made in 27 obese women (BMI : 31.1 +/- 4.9) assigned to 1 of 3 groups: control (C; n = 9), diet only (D O; n = 9), or diet plus aerobic exercise (DE; n = 9). Results: After the 16-wk intervention, changes in body mass (BM) averaged 0 .5 +/- 2.0, -7.2 +/- 7.4, and -4.0 +/- 3.3 kg and changes in %BFd,w,m avera ged 2.1 +/- 1.0%, -1.2 +/- 1.4%, and -2.4 +/- 1.6% in the C, DO, and DE gro ups, respectively. Compared with changes in %BFd,w,m, the errors (SD of bia s) for estimates of changes in %BF by DXA, BIA, SFTs, and BMI were similar (range: +/-2.0-2.4% of BM). BIA, SFTs, and BMI provided unbiased estimates of decreases in % BFd,w,m, but DXA overestimated decreases in %BF in the DO and DE groups. Conclusions: DXA, BIA, SFTs, and BMI are comparably accurate for evaluating body-composition changes induced by diet and exercise interventions; howev er, small changes in %BF may not be accurately detected by these clinical m ethods.