Leucine is an essential amino acid that is also part of the branched chain amino acid (BCCA).
Leucine is an α-amino acid that is used in the biosynthesis of proteins. It is essential in humans, meaning the body cannot synthesize it and must be obtained from the diet. It is in a group of essential amino acids identified as the branched-chain amino acids, BCAAs.
Branched chain amino acids (Leucine, Isoleucine, and valine) are amino acids whose carbon structure is marked by a branch point. These three amino acids are critical to human life and are particularly involved in stress, energy and muscle metabolism.
Despite their structural similarities, the branched amino acids have different metabolic routes, with valine going solely to carbohydrates, leucine solely to fats and isoleucine to both. The different metabolism accounts for different requirements for these essential amino acids in humans.
L-leucine is soluble (in water) and a moderately acidic compound (based on its pKa). L-leucine can be found primarily in most bio fluids, including blood, cerebrospinal fluid (CSF), and sweat, as well as throughout most human tissues. Within the cell, L-leucine is primarily located in the mitochondria. It can also be found in the extracellular space.
Leucine is important for protein synthesis and many metabolic functions.
Leucine is important for protein synthesis and many metabolic functions. It contributes to regulation of blood-sugar levels; growth and repair of muscle and bone tissue; growth hormone production; and wound healing. Leucine also prevents breakdown of muscle proteins after trauma or severe stress and may be beneficial for individuals with phenylketonuria.
In healthy individuals, approximately 60% of dietary L-leucine is metabolized after several hours, with roughly 5% (2–10% range) of dietary L-leucine being converted to β-Hydroxy β-methyl butyric acid (HMB). Around 40% of dietary L-leucine is converted to acetyl-CoA, which is subsequently used in the synthesis of other compounds.
BCAAs, particularly leucine, stimulate protein synthesis, increase reutilization of amino acids in many organs and reduce protein breakdown. Furthermore, leucine can be an important source of calories, and is superior as fuel to the ubiquitous intravenous glucose (dextrose). Leucine also stimulates insulin release, which in turn stimulates protein synthesis and inhibits protein breakdown. These effects are particularly useful in athletic training.
Hemp seed is a good source of leucine.
Human dietary sources are foods that contain protein with leucine as a component. Some of these with content of leucine per 100g include;
Huntington's chorea and anorexic disorders both are characterized by low serum BCAA.
Leucine is available in many foods and deficiency is rare. However, there can be abnormalities that may arise as a result of poor metabolism of leucine or the other branched chain amino acids. A wide range of symptoms, can include mental retardation, ataxia, hypoglycemia, spinal muscle atrophy, rash, vomiting and excessive muscle movement. Most forms of BCAA metabolism errors are corrected by dietary restriction of BCAA and at least one form is correctable by supplementation with 10 mg of biotin daily.
Huntington's chorea and anorexic disorders both are characterized by low serum BCAA. These diseases, as well as forms of Parkinson's, may respond to BCAA therapy. BCAA, and particularly leucine, are among the amino acids most essential for muscle health.
A high intake of leucine may cause or exacerbate symptoms of pellagra.
Leucine toxicity, as seen in decompensated maple syrup urine disease, causes delirium and neurologic compromise, and can be life-threatening.
A high intake of leucine may cause or exacerbate symptoms of pellagra in people with low niacin status because it interferes with the conversion of L-tryptophan to niacin.
Leucine at a dose exceeding 500 mg/kg/d was observed with hyperammonemia. As such, unofficially, a tolerable upper intake level (UL) for leucine in healthy adult men can be suggested at 500 mg/kg/d or 35 g/d under acute dietary conditions.
The Food and Nutrition Board (FNB) of the U.S. Institute of Medicine set Recommended Dietary Allowances (RDAs) for essential amino acids in 2002. For leucine, for adults 19 years and older, 42 mg/kg body weight/day.