Branched chain amino acids http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml are made up of the three essential amino acids, L-leucine, L-isoleucine, and L-valine. Branched chain amino acids are not produced in the body and must be obtained from animal and vegetable food sources. These particular amino acids are used in the synthesis of many other vital body proteins. 
The branched chain amino acids make up about one-third of the protein found in muscle, and work together to promote the building, healing, and repair of muscle tissue. Branched chain amino acids appear to be preferentially absorbed by muscle cells. They then undergo transamination and oxidation and serve as an important energy sources for muscles. BCAA supplementation is often used by athletes and body builders to produce an anabolic effect, increase endurance and energy, and heal the muscle damage that can result from intense exercise. [2-5]
Branched chain amino acids prevent muscle catabolism and enhances protein synthesis. Consequently, it may help patients suffering from liver disease, burns, infection, and other traumas. [6, 7] It is theorized that Branched chain amino acids may decrease the accumulation of false neurotransmitters in the brain, which can improve some symptoms of hepatic encephalopathy. [8, 9] Some researchers also believe that BCAAs may protect against neuronal damage from the neuroexcitatory neurotransmitter, glutamate, which can help the adverse symptoms of amytrophic lateral sclerosis (ALS).  However, a number of studies have disputed this finding. [12-15] Branched chain amino acids have also been found to decrease L-phenylalanine levels in the brain, reducing symptoms of tardive dyskensia.  Finally, preliminary research reports that Branched chain amino acids may benefit patients with phenylketonuria (PKU). [17-18]
The best food sources of the three Branched chain amino acids, L-leucine, L-isoleucine, and L-valine, include meats, nuts, soy, and whey proteins. Seperately, the best dietary sources of L-isoleucine include; chicken, chickpeas, eggs, fish, lentils, rye, and most seeds. L-leucine sources include; brown rice, beans, and whole wheat. L-valine sources: dairy products, grain, and mushrooms. 
BCAA supplementation is frequently used by athletes and body builders to improve performance and recovery after workouts. Several studies report that Branched chain amino acids may promote muscle protein synthesis, and help prevent both muscle protein breakdown and muscle glycogen degradation during exercise. [2-5] However, more research is needed to provide evidence that Branched chain amino acids have a positive effect on exercise performance. One study of elite cyclists showed that Branched chain amino acids had little, or no effect on performance. 
High doses of branched chain amino acids are used in hospitals to treat people suffering from burns, infections, and other traumas. This is largely due to the possible anticatabolic properties of these amino acids. Research indicates that Branched chain amino acids may prevent muscle catabolism, enhance protein synthesis, and promote the healing of bones, skin, and muscle tissue in patients suffering from trauma. [6, 7] Branched chain amino acids are often used in the management of liver disease, such as liver cirrhosis, liver cancer, and hepatic encephalopathy. [8-10, 20-22]
However, there is some controversy regarding the role of Branched chain amino acids in hepatic encephalopathy. A double-blind, placebo-controlled study of 22 hepatic encephalopathy patients reported improvement in cerebral function when treated with Branched chain amino acids.  Conversely, other studies conclude that Branched chain amino acids do not improve cerebral function, nor do they decrease mortality. In fact, BCAAs may only be helpful in treating those hepatic encephalopathy patients intolerant to the supplementary dietary proteins needed to achieve proper nitrogen balance. [10, 23]
Branched chain amino acids have been used in the management of amytrophic lateral sclerosis (ALS), although there is some contradicition regarding its use. Preliminary studies suggest that Branched chain amino acids may improve ALS symptoms. A double-blind, randomized, placebo-controlled study showed therapeutic benefits in 22 ALS patients when treated with Branched chain amino acids.  However, later studies have not supported this finding, and have even reported excess mortality and increased loss of pulmonary function in ALS patients treated with Branched chain amino acids. [12-15]
Branched chain amino acids are also used in the management of tardive dyskinesia and phenylketonuria. One small study found a decrease in symptoms in 9 tardive dyskinesia patients treated with BCAA supplementation.  Similarly, another study reported therapeutic benefits with adolescent and young adult phenylketonuria patients treated with Branched chain amino acids. 
Dosages vary, and range from 200 - 300 mg of each BCAA amino daily, to 2-5 grams daily.
Delivery Forms: Tablets, capsules, and powders. [9, 24]
Branched Chain Amino Acid Deficiency
A deficiency in Branched chain amino acids interferes with proper protein synthesis, leading to a lack of vital proteins in the body. This deficiency can cause a host of physical and cognitive problems, ranging from indigestion to depression and stunted growth. Lower levels of Branched chain amino acids have been associated with depression and/or neurological problems in elderly patients as well. Isoleucine deficiency can lead to symptoms similar to those found in hypoglycemia. 
Branched Chain Amino Acid Toxicity
- Branched chain amino acids are contraindicated in people with the metabolic disorders, maple syrup urine disease, and isovaleric acidemia.
- ALS patients should not take Branched chain amino acids, until more research is conducted.
- Pregnant, lactating women, and children should not take supplemental BCAA, unless recommended by a health care provider.
- Excessively high levels of isoleucine may contribute to symptoms of hypoglycemia and pellagra, or increased ammonia levels. Excessively high levels of valine may lead to symptoms such as a skin crawling sensation or hallucinations.
- Always inform your health care provider about the dietary supplements you are taking, since there may be a potential for drug interactions, side effects, or allergy. [1, 9]
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