L-Leucine is an essential amino acid, meaning it cannot be made by the body, and must be acquired through food or dietary supplements. Leucine is classified as a branched-chain amino acid (BCAA). It comprises about 8% of the total amino acid count in your body's protein structures and is the fourth most concentrated amino acid in skeletal muscle tissue.

L-Leucine stimulates muscle protein synthesis and may be the major fuel involved in anabolic (tissue building) reactions. This makes them especially important for body builders and other athletes in sports that demand explosive strength.

The branch chain amino acids valine, leucine, and isoleucine enhance protein synthesis in liver cells and muscle cells and help promote muscle recovery after exercise. They contribute to energy production in the body by being oxidized in the cell's mitochondria. Branch chain amino acids are used by body builders and athletes to produce an anabolic effect and assist in the repair of micro tears in muscle tissue that are a normal result of exercise. Leucine is thought to be the most effective BCAA for preventing the body's burning of muscle stores for energy during intense workouts because it is converted to glucose more quickly than isoleucine and valine.