essential amino acids
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es·sen·tial a·mi·no ac·ids
α-amino acids nutritionally required by an organism that must be supplied in its diet (that is, cannot be synthesized by the organism) either as free amino acid or in proteins.
essential amino acidsA group of eight amino acids (isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine) which are essential for normal growth and development of humans; absence of an essential amino acid results in a negative nitrogen balance. In premature infants, histidine, arginine and cystine are also essential.
es·sen·tial a·mi·no ac·ids(ĕ-sen'shăl ă-mē'nō as'idz)
The α-amino acids nutritionally required by an organism that must be supplied in its diet (i.e., cannot be synthesized by the organism), either as free amino acids or in proteins.
essential amino acidsThose AMINO ACIDS that cannot be synthesized in the body and must be included in the diet. They include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.
amino acidsorganic acids in which one or more of the hydrogen atoms is replaced by the amino group, NH2. They are the end-products of digestion of dietary protein and from them the body synthesizes its own proteins. Within the body amino acids also act as precursors of many other molecules essential for life. Amino acids may be categorized as essential or non-essential. essential amino acids: those that must be provided in the diet since the human body does not have the enzymes for their synthesis; of the 20 amino acids that are present in proteins or as free amino acids in the body, nine are 'essential' (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine). Of these, three are known as branched-chain aminoacids (BCAA): leucine is oxidized to a significant extent during exercise, and tracer studies that follow leucine kinetics are often used as an estimation of protein turnover; isoleucine and valine can also serve as fuel sources. It has been claimed that ingestion of BCAA before and during exercise may improve the physiological and psychological responses, and that BCAA with arginine and/or other amino acids may promote growth hormone release, but other studies do not support this. There are no known toxic effects. See also ergogenic aids, gluconeogenesis; Table 1.
|Substance||Description||Claimed ergogenic effect||Supporting evidence|
|With clear scientific evidence|
|Caffeine||Stimulant in coffee and tea||Improves performance in most events, except very short high-intensity exercise; increases cognitive functioning during exercise.|
|Creatine||Carrier of high-energy phosphates in muscle||Increases the energy reserve, improves strength, reduces fatigue, and increases protein synthesis||Increases intramuscular Cr and PCr; improves performance in repeated sprint bouts (and reported to do so after even a single bout); improves recovery between bouts (but response varies between individuals). Anabolic properties unclear.|
|Buffers||Improves high-intensity exercise performance by limiting decrease in pH in ECF as a whole and indirectly in muscle ICF||Large doses can improve performance|
|With mixed scientific evidence|
|Antioxidant nutrients||Vitamins, especially C and E||Provides protection against muscle damage by reducing oxidative stress||Benefits established at cellular level; no detectable aid to performance|
|Arginine||Amino acid in normal diet||Stimulates release of growth hormone, promoting gain in muscle mass and strength||Some evidence of GH promotion when combined with other amino acids (ornithine, lysine, BCAA); no conclusive evidence of effect when taken alone|
|Branched-chain amino acids (BCAA)||Leucine, isoleucine and valine||No good evidence of improved endurance performance. Evidence of accelerated recovery from muscle fatigue when given with other amino acids during eccentric exercise training|
|Glutamine||Amide of amino acid glutamate||Maintains a healthy immune system during training and improves muscle glycogen resynthesis||Does not affect immune function; possibly affects muscle glycogen resynthesis|
|Glycerol||Component of triacylglycerol molecule||Induces hyperhydration, decreases heat stress, and improves performance||Does have the first two actions, but effects on performance are unclear|
|Lacking scientific support|
|Androstenedione||Synthetic product||Increases testosterone and thus muscle mass and strength, and improves recovery||Does not increase testosterone secretion; has no effect on strength|
|Hydroxy-methyl butyrate (HMB)||Metabolite of the amino acid leucine||Enhances gain in body mass and strength associated with resistance training, and improves recovery||Possible small effects only on lean body mass and strength|
|Boron||Micronutrient present in vegetables and non-citrus fruits||Increases testosterone levels, to improve bone density, muscle mass, and strength||Improves bone mineral density in postmenopausal women; no effect on bone density, muscle mass or strength in men|
|Carnitine||Substance important for fatty acid transport into mitochondria||Improves fat oxidation, helps weight loss||No supporting evidence|
|Choline||Precursor of acetylcholine||Improves performance, decreases fatigue and enhances fat metabolism||No supporting evidence|
|Chromium (chromium picolinate)||Micronutrient that potentiates insulin action||Promotes fat oxidation and muscle building||No supporting evidence|
|Coenzyme Q10||Part of the electron transport chain in the mitochondria||Improves aerobic capacity and cardiovascular dynamics||No supporting evidence|
|Ginseng||Root of the Araliaceous plant||Improves strength, performance, stamina, and cognitive functioning; reduces fatigue||No supporting evidence|
|Inosine||Nucleoside found naturally in brewer's yeast and organ meats||Increases ATP stores, improve strength, training quality, and performance||No supporting evidence|
|Medium-chain triacylglycerols (MCT)||Triglycerides containing fatty acids with a carbon chain length of 6-10||Improves energy supply, reduces rate of muscle glycogen breakdown, and improves performance||No supporting evidence|
|Pyruvate||End-product of aerobic glycolysis||Improves endurance capacity and recovery; increases glycogen storage||Limited supporting evidence|
|Polylactate||Polymer of lactate||Provides energy||No effects on performance|
|Wheat germ oil||Wheat embryo extract||Improves endurance||No supporting evidence|