Racial differences in relative skeletal muscle mass loss during diet induced weight loss in women

OBJECTIVE: It is unclear whether there are race-specific differences in the maintenance of skeletal muscle during energy restriction. We compared changes in relative skeletal muscle index [RSMI (limb lean tissue/height(2))] following: 1) diet alone (DIET); 2) diet + aerobic training (DAT) or; 3) diet + resistance training (DRT). METHODS: Overweight, sedentary African American (AA; n = 72) and European American (EA; n = 68) women were provided an 800 kcal/day diet to reduce BMI < 25 kg/m(2). Regional fat-free mass was measured with DXA. Steady-state VO(2) and heart rate responses during walking were measured. RESULTS: AA women had greater RSMI and preserved RSMI during DIET while RSMI was significantly reduced among EA (EA −3.6% vs. AA +1.1%; p < 0.05). DRT subjects retained RSMI (EA +0.2% vs. AA +1.4%; p=0.05), whereas DAE subjects decreased RSMI (EA −1.4% vs. AA −1.5%; p<0.05). Maintenance of RSMI was related to delta walking ease and economy. CONCLUSIONS: Compared to AA, EA women are less muscular and lose more muscle during weight loss without resistance training. During diet-induced weight loss, resistance training preserves skeletal muscle especially among premenopausal EA women. Maintenance of muscle during weight loss associates with better ease and economy of walking.