Common Names

  • L-leucine
  • Leucinum
  • L-alpha-aminoisocaproic acid
  • Branched-chain amino acid (BCAA)

For Patients & Caregivers

Leucine is an essential amino acid required for muscle growth and maintenance.

Leucine is an amino acid that is not made in the human body and is required for muscle maintenance. Therefore, it has to be obtained through dietary sources rich in protein such as dairy, soy, and meats. Leucine is also available as a dietary supplement and is used to improve muscle strength and endurance.

Studies done on leucine show that it improves muscle strength but is not useful in the treatment of sarcopenia (loss of skeletal muscle mass and strength). Leucine can also increase secretion of insulin but did not improve sugar levels in diabetic patients.

  • Muscle strength and endurance
    Some studies show that leucine improves muscle strength and endurance.
  • Diabetes
    In one study, leucine did not affect blood sugar level in diabetic men. Further research is needed.
  • Sarcopenia
    Long-term studies do not support use of leucine for the treatment of loss of skeletal muscle mass and strength.
  • You are taking insulin and other antidiabetic medications: Leucine can stimulate insulin secretion and may further lower blood glucose levels.
  • You are taking vitamin B3 and vitamin B6: Leucine can interfere with the production of these vitamins.
  • You have maple syrup urine disease: Leucine can accumulate in blood or urine resulting in dysfunction of nerve cells.
  • May lower blood glucose levels
  • Rare: May cause vitamin B3  and vitamin B6 deficiencies with excessive intake
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For Healthcare Professionals

2-Amino-4-methylpentanoic acid

Leucine is an essential amino acid that is not synthesized in human bodies and must be obtained from food consisting of plant or animal protein. Leucine is often used together with valine and isoleucine, which are branched-chain amino acids, in parenteral forms for nutritional support to maintain nitrogen balance, and to treat cirrhosis and hepatic encephalopathy.

Purified leucine is marketed as a dietary supplement for body building. It is thought to stimulate protein synthesis by activating the mammalian target of rapamycin (mTOR) pathway (1) (2). Dietary supplementation with leucine can improve performance (3) and upper body strength in athletes (4). However, it does not prevent or treat sarcopenia (16) nor affect glycemic control in diabetic men (5).

Because leucine can enhance the proliferation of hematopoietic progenitors, there is current interest in developing it as a treatment for Diamond-Blackfan anemia and for myelodysplastic syndrome (6) (7).
Leucine from dietary sources is generally considered safe. However, excessive intake may result in hypoglycemia (8) and may also cause vitamin B3 and B6 deficiencies (9) (10). Amounts exceeding ∼39 g/d may pose a health risk (17).

Plant and animal proteins

  • Muscle strength
  • Endurance
  • Diabetes
  • Sarcopenia

Leucine stimulates protein synthesis by activating the mammalian target of rapamycin (mTOR) pathway (1). It is thought to enhance muscle anabolic signaling (11). In Diamond-Blackfan anemia patients, L-leucine modulates protein synthesis by enhancing translation leading to improved hemoglobin levels (7). In the presence of glucose, oral leucine ingestion can stimulate insulin secretion and lower blood glucose levels (8).

  • Patients with maple syrup urine disease should not consume leucine and other branched-chain amino acids as they can accumulate in blood or urine causing neuronal dysfunction (15).
  • Rare: Excessive intake of dietary leucine may cause vitamin B3 and vitamin B6 deficiencies (9) (10).
  • Insulin and other antidiabetic medications: Leucine can stimulate insulin secretion and may have additive hypoglycemic effects (8).
  • Vitamin B3 and vitamin B6: Leucine can interfere with synthesis of these vitamins (9) (10).
  • May lower blood glucose levels (8).

  1. Thomson JS, Ali A, Rowlands DS. Leucine-protein supplemented recovery feeding enhances subsequent cycling performance in well-trained men. Appl Physiol Nutr Metab. Apr 2011;36(2):242-253.

  2. Crowe MJ, Weatherson JN, Bowden BF. Effects of dietary leucine supplementation on exercise performance. Eur J Appl Physiol. Aug 2006;97(6):664-672.

  3. Leenders M, Verdijk LB, van der Hoeven L, et al. Prolonged leucine supplementation does not augment muscle mass or affect glycemic control in elderly type 2 diabetic men. J Nutr. Jun 2011;141(6):1070-1076.

  4. Virgilio M. Treatment of Zebrafish Models of Ribosomopathies (Diamond Blackfan Anemia (DBA) and 5q- Syndrome) with L-Leucine Results In An Improvement of Anemia and Developmental Defects: Evidence for a Common Pathway? Paper presented at: American Society of Hematology Annual Meeting2010; Orange County Convention Center.

  5. Jaako P. Bone Marrow Failure in RPS19-Deficient Mice Is Partly Caused by p53 Activation and Responds to L-Leucine Treatment. Paper presented at: American Society of Hematology Annual Meeting2011; San Diego Convention Center.

  6. Kalogeropoulou D, Lafave L, Schweim K, et al. Leucine, when ingested with glucose, synergistically stimulates insulin secretion and lowers blood glucose. Metabolism. Dec 2008;57(12):1747-1752.

  7. Bapurao S, Krishnaswamy K. Vitamin B6 nutritional status of pellagrins and their leucine tolerance. Am J Clin Nutr. May 1978;31(5):819-824.

  8. Glynn EL, Fry CS, Drummond MJ, et al. Excess leucine intake enhances muscle anabolic signaling but not net protein anabolism in young men and women. J Nutr. Nov 2010;140(11):1970-1976.

  9. Cortiella J, Matthews DE, Hoerr RA, et al. Leucine kinetics at graded intakes in young men: quantitative fate of dietary leucine. Am J Clin Nutr. Oct 1988;48(4):998-1009.

  10. Yudkoff M, Daikhin Y, Nissim I, et al. Brain amino acid requirements and toxicity: the example of leucine. J Nutr. Jun 2005;135(6 Suppl):1531S-1538S.

  11. Yudkoff M, Daikhin Y, Grunstein L, et al. Astrocyte leucine metabolism: significance of branched-chain amino acid transamination. J Neurochem. Jan 1996;66(1):378-385.

  12. 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. Mar 30 2004;122(2):180-187.

  13. van Loon LJ. Leucine as a pharmaconutrient in health and disease. Curr Opin Clin Nutr Metab Care. 2012 Jan;15(1):71-7.

  14. Pencharz PB, Elango R, Ball RO. Determination of the tolerable upper intake level of leucine in adult men. J Nutr. 2012 Dec;142(12):2220S-4S.

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