Branched-chain amino acid
A branched-chain amino acid (BCAA) is an amino acid having aliphatic side-chains with a branch (a central carbon atom bound to three or more carbon atoms). Among the proteinogenic amino acids, there are three BCAAs: leucine, isoleucine and valine. Non-proteinogenic BCAAs include norvaline and 2-aminoisobutyric acid.
The three proteinogenic BCAAs are among the nine essential amino acids for humans, accounting for 35% of the essential amino acids in muscle proteins and 40% of the preformed amino acids required by mammals.
Dietary BCAA supplementation has been used clinically to aid in the recovery of burn victims. A 2006 paper suggests that the concept of nutrition supplemented with all BCAAs for burns, trauma, and sepsis should be abandoned for a more promising leucine-only-supplemented nutrition that requires further evaluation. 
Dietary BCAAs have been used in an attempt to treat some cases of hepatic encephalopathy. They can have the effect of alleviating symptoms, but there is no evidence they benefit mortality rates, nutrition or overall quality of life.
Certain studies suggested a possible link between a high incidence of amyotrophic lateral sclerosis among professional American football players and Italian soccer players, and certain sports supplements including BCAAs. In mouse studies, BCAAs were shown to cause cell hyper-excitability resembling that usually observed in ALS patients. The proposed underlying mechanism is that cell hyper-excitability results in increased calcium absorption by the cell and thus brings about cell death, specifically of neuronal cells which have particularly low calcium buffering capabilities. Yet any link between BCAAs and ALS remains to be fully established. While BCAAs can induce a hyperexcitability similar to the one observed in mice with ALS, current work does not show if a BCAA-enriched diet, given over a prolonged period, actually induces ALS-like symptoms.
Blood levels of the BCAAs are elevated in obese, insulin resistant humans and in mouse and rat models of diet-induced diabetes, suggesting the possibility that BCAAs contribute to the pathogenesis of obesity and diabetes. BCAA-restricted diets improve glucose tolerance and promote leanness in mice, and promotes insulin sensitivity in obese rats.
Degradation of branched-chain amino acids involves the branched-chain alpha-keto acid dehydrogenase complex (BCKDH). A deficiency of this complex leads to a buildup of the branched-chain amino acids (leucine, isoleucine, and valine) and their toxic by-products in the blood and urine, giving the condition the name maple syrup urine disease.
The BCKDH complex converts branched-chain amino acids into Acyl-CoA derivatives, which after subsequent reactions are converted either into acetyl-CoA or succinyl-CoA that enter the citric acid cycle.
Claims in Bodybuilding
Bodybuilders make claims about the effectiveness of using BCAAs to aid recovery after a workout. These claims include prolonged mental and physical stamina as well as a decrease in exercise-induced muscle breakdown and inflammation. BCAAs are sold as bodybuilding supplements.
- Sowers, Strakie. "A Primer On Branched Chain Amino Acids" (PDF). Huntington College of Health Sciences. Retrieved 22 March 2011.
- Shimomura Y, Murakami T, Naoya Nakai N, Nagasaki M, Harris RA (2004). "Exercise Promotes BCAA Catabolism: Effects of BCAA Supplementation on Skeletal Muscle during Exercise". J. Nutr. 134 (6): 1583S–1587S. Retrieved 22 March 2011.
- De Bandt JP; Cynober L (2006). "Therapeutic use of branched-chain amino acids in burn, trauma, and sepsis". J. Nutr. 1 Suppl. 136 (30): 8S–13S. Retrieved 22 March 2011.
- Chadalavada R, Sappati Biyyani RS, Maxwell J, Mullen K (2010). "Nutrition in hepatic encephalopathy". Nutr Clin Pract. 25 (3): 257–64. doi:10.1177/0884533610368712.
- Gluud LL, Dam G, Les I, Córdoba J, Marchesini G, Borre M, Aagaard NK, Vilstrup H (2015). "Branched-chain amino acids for people with hepatic encephalopathy". Cochrane Database of Systematic Reviews. (2): CD001939. doi:10.1002/14651858.CD001939.pub2. PMID 25715177.
- Manuel, Marin; Heckman, C.J. (2011). "Stronger is not always better: Could a bodybuilding dietary supplement lead to ALS?". Experimental Neurology. 228 (1): 5–8. doi:10.1016/j.expneurol.2010.12.007. ISSN 0014-4886.
- Lynch, Christopher J.; Adams, Sean H. (2014-12-01). "Branched-chain amino acids in metabolic signalling and insulin resistance". Nature Reviews. Endocrinology. 10 (12): 723–736. doi:10.1038/nrendo.2014.171. ISSN 1759-5037. PMC . PMID 25287287.
- Newgard, Christopher B.; An, Jie; Bain, James R.; Muehlbauer, Michael J.; Stevens, Robert D.; Lien, Lillian F.; Haqq, Andrea M.; Shah, Svati H.; Arlotto, Michelle (2009-04-01). "A branched-chain amino acid-related metabolic signature that differentiates obese and lean humans and contributes to insulin resistance". Cell Metabolism. 9 (4): 311–326. doi:10.1016/j.cmet.2009.02.002. ISSN 1932-7420. PMC . PMID 19356713.
- Fontana, Luigi; Cummings, Nicole E.; Arriola Apelo, Sebastian I.; Neuman, Joshua C.; Kasza, Ildiko; Schmidt, Brian A.; Cava, Edda; Spelta, Francesco; Tosti, Valeria (2016-06-21). "Decreased Consumption of Branched-Chain Amino Acids Improves Metabolic Health". Cell Reports. 16: 520–30. doi:10.1016/j.celrep.2016.05.092. ISSN 2211-1247. PMC . PMID 27346343.
- White, Phillip J.; Lapworth, Amanda L.; An, Jie; Wang, Liping; McGarrah, Robert W.; Stevens, Robert D.; Ilkayeva, Olga; George, Tabitha; Muehlbauer, Michael J. "Branched-chain amino acid restriction in Zucker-fatty rats improves muscle insulin sensitivity by enhancing efficiency of fatty acid oxidation and acyl-glycine export". Molecular Metabolism. 5 (7): 538–551. doi:10.1016/j.molmet.2016.04.006.
- Sears DD, Hsiao G, Hsiao A, Yu JG, Courtney CH, Ofrecio JM, Chapman J, Subramaniam S (2009). "Mechanisms of human insulin resistance and thiazolidinedione-mediated insulin sensitization". Proc. Natl. Acad. Sci. USA. 106 (44): 18745–18750. doi:10.1073/pnas.0903032106. Retrieved 22 March 2011.
- "BCAA Supplements and Their Benefits". Macrospective. Retrieved 2016-03-23.
- Blomstrand, E.; Hassmén, P.; Ekblom, B.; Newsholme, E. A. (1991-01-01). "Administration of branched-chain amino acids during sustained exercise--effects on performance and on plasma concentration of some amino acids". European Journal of Applied Physiology and Occupational Physiology. 63 (2): 83–88. doi:10.1007/bf00235174. ISSN 0301-5548. PMID 1748109.
- Howatson, Glyn; Hoad, Michael; Goodall, Stuart; Tallent, Jamie; Bell, Phillip G.; French, Duncan N. (2012-01-01). "Exercise-induced muscle damage is reduced in resistance-trained males by branched chain amino acids: a randomized, double-blind, placebo controlled study". Journal of the International Society of Sports Nutrition. 9: 20. doi:10.1186/1550-2783-9-20. ISSN 1550-2783. PMC . PMID 22569039.