Effects of diet and exercise on the density and composition of the fat-free mass in obese women

Purpose: The purpose of this study was to determine whether the density (D- FFM) and composition of the fat-free mass (FFM) and the accuracy of estimat es of body composition from body density (%Fat(d)) are affected by diet and exercise, Methods: Twenty-nine obese women (body mass index (BMT) = 25.0-43.7 kgm(-2) and %Fat, = 35.7-47.1%) were assigned to one of three groups: diet only (D O, N = 9); diet and aerobic exercise (DE, N = 9); or control (C, N = Il). M easures of body density by hydrostatic weighing, body water by deuterium di lution, and bone mineral by whole-body dual-energy x-ray absorptiometry, an d estimates of body composition from body density and from a four-component model were obtained before and after a 16-wk diet and exercise interventio n. Results: Mean (+/- SD) changes in body mass were -7.2 +/- 7.4, -3.9 +/- 3.3 , and +1.2 +/- 2.8 kg for the DO, DE, and C, respectively. The density and composition of the FFM did not change significantly (P > 0.05) in any of th e groups. Individual changes in D-FFM (-0.011 to +0.011 g.mL(-1)), and diff erences between changes in %Fat estimated using a four-component model and %Fat(d) (-2.1 to +2.7% body mass) were not related to changes in body mass (r = -0.08). Individual changes in D-FFM were most strongly related to chan ges in water fraction (r = -0.95) and protein fraction (r = +0.88), and wer e unrelated to changes in the mineral fraction (r = +0.04) of the FFM. Conclusions: We conclude that in obese women, the density and composition o f the FFM are unaltered and densitometry correctly assesses group mean chan ges in body composition with moderate weight loss induced by dirt or diet a nd aerobic exercise. However, individual deviations in D-FFM from the assum ed value of 1.1 g.mL(-1) are substantial, and a multi-component model in wh ich body water is measured is needed to accurately assess individual body c omposition changes resulting from diet and exercise.