Nonessential Micronutrient



Leucine is an essential branched-chain amino acid (BCAA) used as an energy source for muscles. A building block of protein (as are all amino acids), leucine plays a vital role in immune-system function as well as muscle protection, fuel, and repair.

Other names for Leucine

L-leucine, D-leucine

Where to find Leucine

All protein-rich foods contain some amount of leucine — dairy products and red meat contain the highest amounts. Whey and egg protein supplements as well as brown rice, beans, nuts, soy flour, and whole wheat are also rich sources.

Popup: Foods highest in Leucine


Why athletes use Leucine

Active people may use leucine (together with valine and isoleucine) to help boost gains in muscle mass since 90% of dietary leucine can be used by muscles for energy. Nonetheless, requirements for leucine are often met with whey protein powder products. And, many athletes find leucine’s metabolite HMB has greater effects on muscle performance.

Ways that Leucine can enhance Muscle Gain & Recovery:
  • Promote muscle recovery and protect muscle tissue from breakdown
  • Prevent muscle loss, especially at high altitudes
  • Increase growth hormone production and help maintain favorable testosterone levels in men
Ways that Leucine can enhance Energy & Endurance:
  • Increase available fuel for muscle cells and preserve muscle energy stores


Signs of Leucine deficiency

Deficiency of Leucine has been linked to:

  • Catabolism (muscle wasting)
  • Increased risk of high blood sugar
  • Hypoglycemia in infants
  • Impaired healing of wounds
Potential uses for Leucine

Research indicates that Leucine may also be useful in the treatment of:

  • Liver disorders
  • Chronic renal failure
  • Allergies
  • Catabolism (muscle wasting)


More about Leucine

Leucine is one of the three “branched-chain” amino acids (BCAA’s), along with isoleucine and valine. These three amino acids account for one third of all the protein in muscle tissue, and this significant contribution makes them highly important for helping build muscle and increase energy in muscle cells. They are also converted to other amino acids when deficiencies arise.

Essential for optimal muscle functioning

Leucine is one of the essential amino acids — that is, we must obtain it from food and/or supplementation. Our muscles use leucine directly for fueling any work they perform, and it has been shown to help prevent muscle breakdown and increase energy and endurance. Leucine may also stimulate insulin release and help stabilize or lower blood sugar levels.

Muscles use leucine both during exercise and when resting, and research has indicated it’s the most important BCAA for energy production. In fact, researchers estimate that up to 90% of dietary leucine is used for energy during exercise and consider it the limiting amino acid when athletes don’t consume additional amounts to make up for what’s used by the body.

In regard to protein metabolism and muscle growth, leucine has been researched more than any of the other amino acids, with the huge exception of glutamine. It’s been shown to help inhibit muscle loss after severe trauma, such as surgery, as well as increasing muscle growth and performance in healthy people. However, much of the interest around leucine is now focused on its metabolites KIC and HMB.

Therapeutic uses

Leucine is also necessary for wound recovery of the skin and bones because it helps protect muscle tissue and stimulate protein synthesis. Senior athletes should also take note that people in their age group are frequently deficient in this important nutrient. This is important because leucine’s been shown to help prevent the muscle wasting that naturally occurs with increased age.

Interestingly, leucine has been studied recently for its potential abilities to help with the treatment of ALS (Lou Gehrig’s Disease). It was, in fact, found to help people with this horrible, debilitating disease retain their muscle strength and even their ability to walk. It also has been found to be helpful for people with a form of liver damage. Again it was found to help prevent muscle wasting. But it was also able to help stimulate the brain messengers in people with this disease and help prevent some of the neurological effects.

Recent research also showed that the three branch-chained amino acids together can reduce muscle wasting (at least slightly) even in people who are bed-ridden.

Pain relief?

Like the amino acid phenylalanine, L-leucine has a mirror image, D-leucine, which has recently been discovered to have similar effects to D-phenylalanine in that it may help lower the breakdown of the body’s natural pain killers and thus ultimately act as a pain killer.

In conclusion

Leucine is an important amino acid that may help a variety of people achieve their goals. However, it will always have a prominent role in muscle metabolism and thus a special place in the hearts (or muscles) of athletes.



The branched-chain amino acids (BCAA’s) are often supplemented together — 5 grams of leucine, 4 grams of valine, and 2 grams of isoleucine per day, although our requirements appear to vary depending on bodyweight. Many people fulfill their leucine needs with a quality whey protein product and supplement with the leucine metabolite HMB for muscle-performance benefits.


Typically, the BCAA’s are supplemented in two doses, with one dose a half hour before training and another before sleep because of their potential to stimulate the release of growth hormone.

Synergists of Leucine

Leucine works with the branched-chain amino acids isoleucine and valine to make up about 35% of the amino acid content found in muscles. Many experts contend that it’s important that these three amino acids be balanced.

Safety of Leucine

Extremely high amounts may result in symptoms of low blood sugar.

Toxicity of Leucine

No known toxicity.

Bans and restrictions

None reported.


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