A composition comprising whey protein and optionally Vitamin D and calcium can be administered to an individual to decrease fat deposition in muscle increase muscle density improve or maintain muscle quality and/or treat or prevent muscle weakness. The composition can be administered to an elderly individual or an individual having a condition associated with increased fat infiltration in muscle to treat the condition, such as obesity. Preferably at least a portion of the whey protein is whey protein micelles, and a daily dose of the whey protein is at least 18 g.
