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

Abstract

Background: Most methods available to clinicians for estimating body- composition changes have been validated against estimates from densitometry, based on a 2-component (fat mass and fat-free mass) model. Objective: Estimates of changes in percentage body fat (%BF) from dual-energy X-ray absorptiometry (DXA), skinfold thicknesses (SFTs), bioelectrical impedance analysis (BIA), and body mass index (BMI; in kg/m2) were compared with estimates from a 4-component (fat, water, mineral, and protein) model (%BF(d,w,m)), a more accurate method. Design: Determinations of body density from hydrostatic weighing, body water from deuterium dilution, bone mineral and %BF from whole-body DXA, resistance 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 (DO; 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 %BF(d,w,m) averaged 2.1 ± 1.0%, -1.2 ± 1.4%, and -2.4 ± 1.6% in the C, DO, and DE groups, respectively. Compared with changes in %BF(d,w,m) the errors (SD of bias) 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 %BF(d,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; however, small changes in %BF may not be accurately detected by these clinical methods.