Supplement Ingredient Guide: Leucine

What is it?

Leucine is one of the three Branched Chain Amino Acids which is activates mTOR, a protein which then induces muscle protein synthesis via S6K.

Indications

Leucine is primarily indicated for those looking to stimulate muscle growth. It does so by Target of Rapamycin (TOR) which is known as mTOR in humans. This further activates several pathways which all lead to an increase in skeltal muscle synthesis. In higher doeses it has been shown to attenuate atrophy and maintinaing muscle mass.

How much should I take?

It is normally taken as part of a BCAA complex, although it can be taken on its own. The benifits are dose dependant. The upper safe limit has been set to 500mg/kg per day.

Research

It has been shows that leucine activates mTOR, a protein which then induces muscle protein synthesis via S6K.

Side effects

Studies have not reported any side effects with doses as high as 1250mg/kg.

In conclusion, leucine increases protein synthesis by increasing the activity of mTOR. It has the greatest stimulatory effect on protein synthesis.Adding leucine to a protein-rich meal further increases the rate of skeletal muscle protein synthesis.

References

http://examine.com/supplements/Leucine
Anthony, J. C., Yoshizawa, F., Anthony, T. G., Vary, T. C., Jefferson, L. S., & Kimball, S. R. (2000) Leucine stimulates translation inititation in skeletal muscle of postabsorptive rats via a rapamycin-sensitive pathway. J. Nutr. 130: 2413-2419.
Crozier, S. J., Kimball, S.R., Emmert, S. W., Anthony, J. C., & Jefferson, L.S. (2005) Oral leucine administration stimulates protein synthesis in rat skeletal muscle. J. Nutr. 135: 376-382.
Bolster, D. R., Crozier, S. J., Kimball, S. R., & Jefferson, L. S. (2002) AMP-activated protein kinase suppresses protein synthesis in rat skeletal muscle through down-regulated mammalian target of rapamycin (mTOR) signaling. J. Biol. Chem. 277: 23977-23980.
Merrick, W. C., & Hershey, J. W. B. (2000) The pathway and mechanism of initiation of protein synthesis. In: Sonnenberg N, Hershey JWB, Mathews MB, editors. Translational control of gene expression. Cold Spring Harbor Laboratory Press.*
Koopman R, Wagenmakers AJ, Manders RJ, Zorenc AH, Senden JM, Gorselink M, Keizer HA, van Loon LJ. (2005) Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects. Am. J. Physiol. Endocrinol. Metab. 288(4): E645-653.