Dispensable and indispensable amino acids for humans

Here, we compared the traditional nutritional definition of the dispensable and indispensable amino acids for humans with categorizations based on ami no acid metabolism and function. The three views lead to somewhat different interpretations, From a nutritional perspective, it is quite clear that so me amino acids are absolute dietary necessities if normal growth is to be m aintained. Even so, growth responses to deficiencies of dispensable amino a cids can be found in the literature. From a strictly metabolic perspective, there are only three indispensable amino acids (lysine, threonine and tryp tophan) and two dispensable amino acids (glutamate and serine). In addition , a consideration of in vivo amino acid metabolism leads to the definition of a third class of amino acids, termed conditionally essential, whose synt hesis can be carried out by mammals but can be limited by a variety of fact ors. These factors include the dietary supply of the appropriate precursors and the maturity and health of the individual. From a functional perspecti ve, all amino acids are essential, and an argument in favor of the idea of the critical importance of nonessential and conditionally essential amino a cids to physiological function is developed.