A method and composition for preserving muscle mass and function by increasing muscle protein synthesis and/or decreasing muscle protein degradation in mammals is disclosed. In one embodiment, the mammals are administered a protein building composition comprising at least two of an essential amino acid, an amino acid derivative, and a nitrogenous organic acid. In a particular embodiment, the protein building composition comprises leucine, L-carnitine, and creatine. The protein building composition can decrease TNF-α and increase mTOR expression in muscle.
