Leucine, like its cousins isoleucine and valine, is a hydrophobic amino acid that is found as a structural element on the interior of proteins and enzymes. There appears to be no other significant metabolic role for these amino acids, but they are essential and because they are not synthesized by mammalian tissues, must be taken in the diet. Leucine ties glycine for the position of second most common amino acid found in proteins with a concentration of 7.5 percent on a molar basis compared to the other amino acids.

Leucine is an essential amino acid. Only the L form of amino acids are constituents of protein. Leucine is essential for growth, stimulates the production of muscle tissue, and protects the liver from the damaging affects of alcohol.

Leucine helps with the regulation of blood-sugar levels, the growth and repair of muscle tissue (such as bones, skin and muscles), growth hormone production, wound healing as well as energy regulation. It can assist to prevent the breakdown of muscle proteins that sometimes occur after trauma or severe stress. It may also be beneficial for individuals with phenylketonuria - a condition in which the body cannot metabolize the amino acid phenylalanine.

Deficiency of this nutrient is rare, since all protein foods contain it, but vegans and vegetarians without adequate protein sources may suffer from a deficiency. Hypoglycemia symptoms may appear if the diet is deficient and may include dizziness, fatigue, headaches, irritability, etc.

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

If you are taking a supplement of leucine, keep it in balance with the other two branched-chain amino-acids isoleucine and valine in the formula of 2 mg of leucine and valine for each 1 mg of isoleucine.

Leucine is found in protein foods, as well as brown rice, beans, nuts and whole wheat.