L-Leucine is one of the three BCAAs that is critical in muscle tissue structure. Leucine is a signaling molecule that helps to regulate optimal skeletal muscle protein synthesis in normal tissues. In addition, it helps to maintain already healthy glucose metabolism and insulin function, and may help to promote the use of fat for energy. Studies suggest that L-Leucine, in conjunction with adequate dietary protein, may help to build and maintain lean tissue and optimize body composition.