What it is:
Leucine is one of three branched chained amino acids (BCAA) that are part of the essential amino acid group. The chemical formula of leucine is C6H13NO2. The chemical names for leucine are 2-amino-4-methylvaleric acid, alpha-aminoisocaproic acid, and (S)-2-amino-4-methylpentanoic acid. Though these names may make leucine sound complicated, its role as a supplement seems to be fairly straightforward.
Where it comes from:
Leucine is found in both plant and animal protein. Some of the major sources are eggs, pork, beef and soy. Leucine may also be found in leafy vegetables as well as vegetable juices. Fermented foods such as yogurt and miso also contain leucine.
Leucine is largely used to help prevent mental fatigue during prolonged periods of physical stress. It has been shown that mental fatigue adversely affects physical performance. This theory is known as the “Central Fatigue” Theory. Basically, when the body is put under prolonged physical stress the concentration of branched chained amino acids in the blood drops, which creates an increase in fatty acid levels for additional energy support. Fatty acids attach to Albumin for transport. A chemical known as tryptophan also uses Albumin for transport and is displaced by the abundant fatty acids that are present. This displacement causes more tryptophan to cross into the brain. Tryptophan is a well known precursor to serotonin. Serotonin is a neurotransmitter in the brain which depresses the Central Nervous System(CNS). This depression of the CNS causes sleepiness or fatigue, which may decrease athletic performance. Leucine is then supplemented to increase the concentration of BCAAs in the blood and compete with tryptophan for passage into the brain.
Leucine has also been found to support protein synthesis. A study done on rats showed that supplementation of leucine at very high levels increased protein synthesis and inhibited protein degradation. This may have been brought about by an increase in serum insulin levels due to an increase in leucine. It was theorized that the physiological role of leucine is to work with insulin to “activate a switch” which will stimulate protein synthesis.
The recommended dosage is usually given for total amounts of BCAAs because it would not be as beneficial to only supplement with leucine. Therefore, it is recommended that an athlete use 10-20 grams of total BCAAs per day. These dosages should be divided up and taken 3-5 times during the day while concentrating the higher dosages before, during, and after exercise. When taking BCAAs before and during exercise, it is best to supplement 1-7 grams per liter of a carbohydrate containing fluid. Post exercise should constitute 750-1500 mg of total BCAAs. The ratio of the BCAAs should be 3:1:1 Leucine, Valine, and Isoleucine respectively.
There have been few reports of gastrointestinal distress with extremely high amounts of leucine, or total BCAAs consumed. Though in the studies with the protein synthesis in the rats, the scientists conducting the study implied that prolonged high dosages of leucine may lead to insulin resistance (Type II Diabetes Mellitus) which may lead to slowing of protein synthesis stimulation by food uptake. Though overall no significant side effects have been found for leucine at moderate to high levels.
Supplement Watch – http://supplementwatch.com/suplib/supplement.asp?DocId=2403
Garlick, Peter J. The Role of Leucine in the Regulation of Protein Metabolism 1,2.