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What is leucine?

Find out more about essential amino acids

Leucine is an essential amino acid and makes up approximately eight percent of the body’s protein structures. It is one of the three branched-chain amino acids (BCAAs). The body uses it for muscle repair and growth together with isoleucine and valine.

This amino acid helps to sustain nitrogen balance and energy supply during times of stress. These qualities make this amino acid particularly important for body builders and other athletes that require strength and stamina.

Health benefits

Building muscle

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Of the three BCAAs, leucine is considered the most important because it has the most influence over muscle building. This is because it prevents muscle breakdown and facilitates muscle synthesis.

Leucine can also help with weight loss. Scientists have shown that it can burn visceral fat deposits 1. This helps to support a leaner body mass with increased muscle; both important factors for athletes.


Leucine plays a very important role in regulating blood sugar levels. Studies have shown that increases in dietary leucine can reduce diet-induced obesity, hyperglycemia, and cholesterol levels in animals2, 3. There is evidence to suggest that this amino acid may have a role to play in preventing diabetes4.

Scientists are also investigating the role leucine has in patients with diabetes. As this amino acid can help to improve protein synthesis, there is a theory suggesting people with insulin-dependent diabetes may benefit from increasing their intake of leucine to counteract protein degradation.

There is some evidence that this amino acid can help to slow muscle wasting in people with diabetes and improve glucose homeostasis 5, 6, 7. However this research is still under development and more in-depth longitudinal clinical studies are necessary.


Sarcopenia is a condition where the skeletal muscle mass protein content declines and skeletal muscle fat levels increase. This occurs as the body ages and is believed to be associated with a reduction in the metabolic reaction to leucine protein synthesis8.

Sarcopenia makes people frail and more susceptible to injury. There is some evidence to suggest that increasing dietary intake of this amino acid can help to improve muscle protein synthesis in the elderly9.

Injury recovery

BCAAs are important for helping the body to recovery following injury. Leucine helps to promote the healing of muscle tissue, skin, and bones following trauma.

Scientists often recommend that people recovering from surgery take BCAA supplements or eat a diet rich in these amino acids to accelerate healing.

Leucine deficiency or excess

Leucine deficiency is rare. When it does occur, symptoms include dizziness, headaches, depression, confusion, fatigue, and irritability. On the other hand, an excess amount can impair liver and kidney function, plus predispose people to developing pellagra.

Dietary sources and supplements

nuts with l-leucine

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Leucine is found naturally in foods such as beans, brown rice, meat, nuts, whole wheat and soy flour. Most protein rich foods contain this essential amino acid.

Doctors may recommend supplements to people who have a low protein diet or exercise a lot. You should take this amino acid together with isoleucine and valine to help the body use it effectively. There are a wide range of BCAA supplements available which have the right ratio of these amino acids to support a healthy body.

As with any supplementation program, always consult a health physician before taking BCAA supplements to rule out any underlying adverse health effects.


  1. Yeh Y (1984). Ketone body synthesis from leucine by adipose tissue from different sites in the rat. Archives of Biochemistry and Biophysics. Volume 233, Issue 1, pp. 10-8.
  2. Zhang Y, et al. (2007). Increasing Dietary Leucine Intake Reduces Diet-Induced Obesity and Improves Glucose and Cholesterol Metabolism in Mice via Multimechanisms. Diabetes. Volume 56, Issue 6, pp (1647-54)
  3. Escobar J, et al (2005). Physiological rise in plasma leucine stimulates muscle protein synthesis in neonatal pigs by enhancing translation initiation factor activation. The American Journal of Physiology. Volume 288, Issue 5, (pp. E914-E921).
  4. Gua, K. et al. (2010). Chronic leucine supplementation improves glycemic control in etiologically distinct mouse models of obesity and diabetes mellitus. Nutrition and Metabolism. Volume 7, Issue 57, doi: 10.1186/1743-7075-7-57.
  5. Godil, M. et al. (2005). Effect of Insulin with Concurrent Amino Acid Infusion on Protein Metabolism in Rapidly Growing Pubertal Children with Type 1 Diabetes. Pediatric Research. Volume 58, (pp. 229-34)
  6. Leenders, M. and van Loon, J. (2011). Leucine as a pharmaconutrient to prevent and treat sarcopenia and type 2 diabetes. Nutrition Reviews. Volume 69, Issue 11, (pp. 675-89).
  7. Pedroso, J. et al. (2015). Reviewing the Effects of l-Leucine Supplementation in the Regulation of Food Intake, Energy Balance, and Glucose Homeostasis. Nutrients. Volume 7, Issue 5. (p. 3914-37).
  8. Fujita S. and Volpi, E. (2006). Amino acids and muscle loss with aging. Journal of Nutrition. Volume 136, Issue 1, (pp. 2777S-80S).
  9. Katsanos, C. et al. (2006). A high proportion of leucine is required for optimal stimulation of the rate of muscle protein synthesis by essential amino acids in the elderly. American Journal of Physiology – Endocrinology and Metabolism. Volume 291, Issue 2, (pp. 384-7).