Amino acid: One of the20 building blocks from which proteins are assembled. Isoleucine, leucine, lysine, phenylalanine, threonine, tryptophan, and valine are deemed 'essential' amino acids because the human body cannot make them and they must be obtained in the diet. Amino acids are sometimes taken orally in supplement form.
Quick GuideFat-Burning Foods in Pictures: Blueberries, Green Tea, and More
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Last Editorial Review: 5/13/2016