What is Leucine

Chemical Name: (S)-2-amino-4-methylpentanoic acid

Molecular Weight: 131.17

Structrual Formula:

Nitrogen Content: 10.68%


  • Leucine is one of three branched-chain amino acids (the others are valine and isoleucine) that enhance energy, increase endurance, and aid in muscle tissue recovery and repair. L-Leucine is an essential amino acid and works with isoleucine and valine to protect muscle and act as fuel.
  • This group also lowers elevated blood sugar levels and increases growth hormone production.
  • The three branched-chain amino acids constitute approximately 70 percent of the amino acids in the body proteins. As such, their value in the formation and maintenance of structural and functional integrity in humans is unmeasured.
  • Supplemental valine should always be combined with isoleucine and valine at a respective milligram ratio of 2:1:2.

Function of Leucine (254)

  • Helps function of isoleucine (another essential amino acid)
  • Required for formation of blood (254)
  • Regulates digestion and metabolism
  • Assists in the function of the glandular system
  • Found to be deficient in alcoholics and drug addicts
  • Essential for blood sugar regulation (254)
  • Supports healing of traumatized areas of skin and bone (250)
  • In excess, can cause low blood sugar levels (254)

Leucine and Liver diseases

  • Appear to be quite helpful in treating
  • In some cases even reversing hepatic encephalopathy, a form of liver damage in alcoholics (251)
  • Lecuine also help curb muscle wasting in this disease and through their actions on brain neurotransmitters, help prevent some adverse neurological effects of chronic liver disease (251)

Leucine and muscles

  • Leucine and the other branched chain amino acids (BCAAs), isoleucine and valine, escape liver metabolism and can directly and significantly influence muscle-protein metabolism (253)
  • Dietary leucine serves as a substrate for muscle metabolism during periods of cellular energy depletion, there by sparing critical contractile and enzyme muscle protein from degradation to supply leucine requirements.(253)
  • Because leucine contributes to glutamine synthesis, taking supplemental leucine before and after intense training and between meals can help normalize glutamine levels in both the serum and muscle, thereby promoting anticatabolic muscle metabolism as well as supporting immune function

Leucine and exercises

  • Leucine supplementation has been reported to decrease exercise-induced protein degradation and/or muscle enzyme release (an indicator of muscle damage) possibly by promoting an anti-catabolic hormonal profile (252)
  • Theoretically, Leucine supplementation during intense training may help minimize protein degradation and thereby lead to greater gains in fat-free mass
  • Although several studies support this hypothesis, additional research is necessary to determine the long-term effects of leucine supplementation during training on markers of catabolism, body composition, and strength. (252)
  • The availability of Leucine during exercise has been theorized to contribute to central fatigue. During endurance exercise, Leucine are taken up by the muscles rather than the liver in order to contribute to oxidative metabolism. The source of Leucine for muscular oxidative metabolism during exercise is the plasma BCAA pool, which is replenished through the catabolism of whole body proteins during endurance exercise. (252)

Toxicity of Leucine

A high intake of leucine could contribute to pellagra as well as increase the amount of ammonia present in the body (255)

The Recommended Daily Allowance of Leucine

Age Group
Infant(3-6 months)
Child (10-12yr)
Requirement — mg per kg of body weight

Leucine in Food

Fish & other seafoods
Sesame seeds
Amount (mg/lb)
2,000 -8,500


  • 254) Hutson, S. M. & Harris, R. A. (2001) Leucine as a nutritional signal. J. Nutr. 131:839-840.
  • 250) Anthony, J. C., Anthony, T. G., Kimball, S. R. & Jefferson, L. S. (2001) Signaling pathways involved in translational control of protein synthesis in skeletal muscle by leucine. J. Nutr. 131:856-860.
  • 251) Stoll B., Burrin D., Henry J, Yu H., Jahoor F., and Reeds P.. Dietary Amino Acids Are the Preferential Source of Hepatic Protein Synthesis in Piglets. J. Nutr. 1998 128: 1517-1524.
  • 253) Funabiki R., Yagasaki K., Hara H., Nyumura N., Yoshizawa F., Saito K. In vivo effect of L-leucine on protein synthesis in mice. J. Nutr. Biochem. 1992;3:401-407 .
  • 252) Dohm G. L., Kasperek G. J., Tapscott E. B., Beecher G. R. Effects of exercise on synthesis and degradation of muscle protein. Biochem. J. 1980;188:255-262.
  • 255) Kasinski A, Doering CB, Danner DJ. Leucine toxicity in a neuronal cell model with inhibited branched chain amino acid catabolism. Brain Res Mol Brain Res. 2004 Mar 30;122(2):180-7.
  • 139) Borsheim, Elisabet, et al. Branched-Chain Amino Acids activate key enzymes in protein synthesis after physical exercise. American Society for Nutrition J. Nutr. 136:269S-273S.
  • 194) Blomstrand Eva, et al. Essential amino acids and muscle protein recovery from resistance exercise. Am J. Physiol Endocrinol Metab 283: E648-E657.
  • 196) Zhang Yiying, et al. Increasing dietary Leucine intake reduces diet-induced Obesity and Improves glucose and cholesterol metabolism in mice via multimechanisms. Diabetes 56: 1647-1654.