Influence of distribution of lean body mass on resting metabolic rate after weight loss and weight regain: comparison of responses in white and black women

BACKGROUND: Little is known about the effect of weight change on regional lean body mass (LBM) distribution or on racial differences in resting metabolic rate (RMR). OBJECTIVE: The study compared total and regional LBM patterns in white and black women after weight loss and regain and assessed the influence of regional LBM on variances in RMR. DESIGN: Eighteen white and 22 black women who did not differ in age, weight, and height were studied 3 times: in the overweight state, after weight reduction to the normal-weight state, and after 1 y without intervention. Total and regional lean and fat masses were assessed by dual-energy X-ray absorptiometry. RESULTS: White and black women did not differ significantly in mean (+/- SD) weight loss (13.4 +/- 3.6 and 12.7 +/- 3.2 kg, respectively) and regain (6.1 +/- 5.5 and 6.4 +/- 5.4 kg, respectively). Black subjects had significantly less trunk LBM and significantly more limb LBM at each time point (P < 0.05). In both races, weight regain was associated with significant increases in limb LBM (P < 0.05) but not in trunk LBM (P = 0.21). RMR, adjusted for total LBM and fat mass, was significantly higher in white women after weight loss (P < 0.01) and regain (P < 0.01). However, no racial difference was found when RMR was adjusted for LBM distribution. CONCLUSIONS: In both races, trunk LBM decreased with weight loss and remained lower, despite significant weight regain, which potentially reflected decreased organ mass. Regional LBM distribution explained the racial difference in RMR.