Some aspects of in vivo human protein and amino acid metabolism, with particular reference to nutritional modulation
Young, V.R.; Fukagawa, N.; Bier, D.M.; Matthews, D.
Verhandlungen der Deutschen Gesellschaft für Innere Medizin 92: 640-665
1986
ISSN/ISBN: 0070-4067 PMID: 3811566 Document Number: 273543
Under usual circumstances, the protein component of the diet serves as the source of amino acids which the body cannot make at a rate commensurate with meeting the metabolic needs of organs and tissues (the nutritionally indispensable or essential amino acids) and provides nitrogen for the synthesis of other amino acids (the nutritionally dispensable or non-essential amino acids) and nitrogen-containing compounds of physiologic and metabolic significance, such as neurotransmitters, creatinine, glutathione and nucleic acids. Where special nutritional therapies are necessary the amino acids and nitrogen can be supplied by formulations designed for either enteral or parenteral administration. In the body, proteins function as organic catalysts (enzymes), are used for the structural formation of cells, act as antibodies, and serve to control cellular metabolism (hormones and protein mediators). An inadequate protein or amino acid intake, due to lower than normal intakes or failure to raise intakes because of increased needs, causes diminished content of protein in cells and organs and deterioration in the capacity of cells to carry out their normal function. This leads to increased morbidity, and eventually death. Thus, an adequate diet, whether consisting of normal foods or specially formulated medical products, must contain an appropriate level of protein (nitrogen) and mixture of amino acids, in addition to major energy yielding substrates (carbohydrate and lipid) and other essential nutrients, including vitamins and minerals, if health is to be maintained and if the prevention of major body protein loss and/or restoration of body tissues during and following disease is to be achieved.