Source Naturals

Free-Form L-Leucine by Source Naturals is a standalone supplement delivering 1.5 g of L-leucine per serving, an essential branched-chain amino acid critical for initiating muscle protein synthesis via mTOR activation. While leucine is a key driver of anabolic signaling—especially in aging or catabolic populations—the dose provided is below the clinically studied range required for optimal efficacy in sarcopenia or resistance training support.