Leucine: the muscle maker

Amino acids are the chemical units or “building blocks” of the body that make up protein. Muscle, tendons, organs, glands, nails and hair are all made up of protein substances and are therefore dependent on protein for growth, repair and maintenance. Leucine is one of three branched chain amino acids (BCAAs) in the body, the other two being isoleucine and valine, and is the fourth most concentrated amino acid in skeletal muscle tissue.

Leucine was first isolated from cheese in an impure form in 1819 and then from muscle and wool in the crystalline state in 1820. It was named after the Greek word leukos (white), because at that time the purification of a substance from nature to a white, crystalline state was considered remarkable.

Leucine, or l-leucine, is classed as an essential amino acid, which means your body cannot synthesise it and it therefore needs to be obtained from your diet. Primary sources of leucine include high-quality protein foods such as beef, dairy products, poultry, fish and eggs. Vegetarian sources include wholegrain wheat, nuts, soy and brown rice. A diet rich in animal protein or a well-composed combination of plant proteins should satisfy the leucine requirements for the average person. However, some individuals may have heightened needs for leucine, such as those wanting to build lean muscle mass or to help athletic performance and recovery.

Versatile leucine

Leucine is the primary regulator of protein synthesis and is the most potent of the branched chain amino acids in regulating protein metabolism. Supplementation with leucine therefore has many clinical applications, particularly where there’s a need for enhanced protein synthesis. Leucine can be used for the prevention and treatment of sarcopenia (loss of muscle mass), recovery from sepsis and burn, the healing of bones, skin and muscle tissue after traumatic injury, and for those recovering from surgery.

Leucine supplementation is also involved in pain relief because of its ability to stimulate the production of endorphins. It potentiates human growth hormone (HGH), which stimulates growth and cell reproduction and plays a role in various metabolic processes such as increased muscle mass, increased bone density, increased energy levels, improved skin tone and improved immune function.

Leucine may help relieve symptoms of fibromyalgia, as this condition is often accompanied by lowered plasma levels of branched chain amino acids (BCAAs). Leucine, in conjunction with isoleucine and valine, has shown efficacy in treating hepatic encephalopathy, a form of liver damage in alcoholics. It can also play a role in the treatment of ALS (amyotrophic lateral sclerosis), a debilitating neuromuscular disease. Research has revealed its positive effect on those with the condition in retaining their muscle strength and improving their ability to walk.

Muscle builder

After the age of 40, humans start losing muscle at about 0.5–2 per cent per year. Leucine supplementation restores a balanced protein metabolism, reduces protein degradation and actually signals the muscle cell to start absorbing protein into the cell. Significant decreases of leucine in blood and muscle occur following aerobic and strength exercise sessions. Research has shown that supplementation of leucine when undertaking intensive training results in increased muscle mass and an accompanying increase in strength. For example, one study showed that leucine supplementation significantly improved endurance performance and upper body power in a group of canoeists.

If you don’t fall into the category of being an experienced athlete or don’t spend hours at the gym every day, but are nevertheless undertaking regular physical exercise, don’t worry. The good news is that leucine supplementation is particularly beneficial for building muscle in those who are classed as “untrained athletes”. It has even shown positive results for people who are not able to partake in any physical exercise or are bedridden and is therefore useful in combating muscle wasting in the elderly.

Belly-fat buster

Leucine supplementation induces a significant reduction of visceral fat, the fat accumulated around your abdominal organs, particularly when used in conjunction with a calorie-restricted diet. Those with visceral fat, or “belly fat”, are more susceptible to heart disease, stroke, diabetes and hypertension. Because of its role in building muscle mass and reducing visceral fat, leucine is extremely valuable in improving body weight composition.

It’s commonly found that those with an accumulation of belly fat also tend to have high blood sugar levels. It’s handy, then, that leucine is also involved in stimulating insulin release from pancreatic beta cells, which makes it useful in lowering elevated blood sugar levels.

Because of its role in insulin release, excessive doses of leucine can cause an overproduction of insulin by the pancreas, particularly in people who already have elevated insulin levels, and can therefore exacerbate hypoglycaemia. Some infants can’t metabolise leucine (or isoleucine or valine), which causes a rare condition known as maple syrup urine disease and should be avoided in these individuals.


Leucine supplementation works best when used in conjunction with other amino acids, particularly the other two branched chain amino acids, isoleucine and valine, as well as with B-complex vitamins. When taking leucine as part of a branched chain amino acid supplement, the ideal amino acid ratio is two parts leucine to one part isoleucine to two parts valine. The recommended dose of leucine is 16mg per kilogram of body weight which, for example, works out to be 1120mg (1.12g) of leucine per day for a person weighing 70kg.

Leucine in action

  • Wound healer
  • Muscle builder
  • Blood sugar regulator
  • Visceral fat buster
  • Pain killer
  • Athletic performance
  • Growth

Saskia Brown is a qualified naturopath. She is currently practising at Neutral Bay Health & Wellbeing and specialises in weight loss, allergies and asthma. T: (02) 9953 8503, W:

The WellBeing Team

The WellBeing Team

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