Amino Acids
A group of organic compounds considered the building blocks of proteins. Of the nearly 80 amino acids found in nature, about 20 are required for human growth and metabolism.
Essential amino acids are those provided by foods; nonessential amino acids are produced naturally by the body and therefore not required though food intake. The essential amino acids are histidine, isoleucine, leucine, lysine, methionine, cysteine, phenylalanine, tyrosine, threomine, tryptophan and valine. The nonessentials are alanine, aspartic acid, arginine, citrulline, glutamic acid, glycine, hydroxyglutamic acid, hydroxyproline, norleucine, proline and serine.
Examples of complete proteins, that is, those containing all the essential amino acids, are milk, milk products, eggs and meat. Vegetables, grains and gelatin are incomplete proteins. in a normal adult maintaining a constant weight, the recommended daily protein intake is about 46 grams of protein per day for women and 56 grams per day for men.
During digestion, amino acids transfer from the walls of the intestine and the portal vein into the blood. From the blood they move through the liver into the bloodstream, and are then distributed to the tissues as required so the tissues can produce their own protein. Amino acids not needed by the body for the building and repair of tissue are broken down into ammonia, carbon dioxide and water, producing heat and energy. They may also become the end products of digestion, such as urea, which is eliminated by the body.
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