PURPOSE: To investigate the effects of 12 months of dietary weight loss and/or aerobic exercise on lean mass and the measurements defining sarcopenia in postmenopausal women, and to examine the potential moderating effect of serum 25-hydroxyvitamin D (25-OH-D) and age. METHODS: 439 overweight and obese postmenopausal women were randomized to: diet modification (n = 118); exercise (n = 117), diet+exercise (n = 117), or control (n = 87). The diet intervention was a group-based program with a 10% weight loss goal. The exercise intervention was 45 mins/day, 5 days/week of moderate-to-vigorous intensity aerobic activity. Total and appendicular lean mass were quantified by dual x-ray absorptiometry (DXA) at baseline and 12 months. A skeletal muscle index (SMI = appendicular lean mass (kg)/m) and the prevalence of sarcopenia (SMI < 5.67 kg/m) were calculated. Serum 25-OH-D was assayed using a competitive chemiluminescent immunoassay. RESULTS: Dietary weight loss resulted in a significant decrease in lean mass, and a borderline significant decrease in appendicular lean mass and SMI compared to controls. In contrast, aerobic exercise significantly preserved appendicular lean mass and SMI. Diet+exercise attenuated the loss of appendicular lean mass and SMI compared to diet alone, and did not result in significant loss of total- or appendicular lean mass compared to controls. Neither serum 25-OH-D nor age were significant moderators of the intervention effects. CONCLUSIONS: Aerobic exercise added to dietary weight loss can attenuate the loss of appendicular lean mass during weight loss, and may be effective for the prevention and treatment of sarcopenia among overweight and obese postmenopausal women.

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