Leucine or L leucine is an essential amino acid, which means the body cannot manufacture it and it must be ingested through dietary protein. Along with other essential amino acids, leucine helps maintain muscle mass -- which has made leucine-containing supplements a favourite with bodybuilders and athletes. A diet rich in the amino acid leucine might help prevent the muscle loss that typically comes with aging. French researchers found that a leucine-supplemented diet restored a more youthful pattern of muscle-protein breakdown and synthesis in elderly rats.Benefits L-Leucine has many beneficial effects on sports performance.It helps preserve lean muscle tissueit supplies the body with energy when under stressit preserves muscle glycogen (glucose stored in muscle tissue used to power muscular contraction)it maintains nitrogen balance and it enhances mental abilities that can decline as physical activity becomes more intense.