Effect of protein supplementation during diet-induced weight loss on muscle mass and strength: a randomized controlled study

OBJECTIVE: High protein (particularly leucine-rich whey protein) intake is recommended to mitigate the adverse effect of weight loss on muscle mass. The effectiveness of this approach is unknown. METHODS: Seventy middle-aged (50–65 y old) postmenopausal women with obesity were randomized to: 1) weight maintenance (WM); or 2) weight loss and the Recommended Daily Allowance (RDA) for protein (0.8 g protein/kg/d; WL group); or 3) weight loss plus whey protein supplementation (total protein: 1.2 g/kg/d; WL-PS group). Thigh muscle volume and strength were assessed at baseline and after 5% and 10% weight loss in the weight loss groups and after matched time periods (~3 and 6 months, respectively) in the WM group. RESULTS: 5% weight loss caused a greater decrease in thigh muscle volume in the WL than the WL-PS group (4.7±0.7% vs 2.8±0.8%, respectively; P<0.05). After 10% weight loss, there was no statistically significant difference in muscle mass loss in the two groups and the total loss was small in both groups (5.5±0.8% and 4.5±0.7%, respectively). The dietary interventions did not affect muscle strength. CONCLUSION: Whey protein supplementation during diet-induced weight loss does not have clinically important therapeutic effects on muscle mass or strength in middle-aged postmenopausal women with obesity.