Essential Amino Acids
Humans can produce 10 of the 20 amino acids. The others must be supplied in the food. Failure to obtain enough of even 1 of the 10, those that we cannot make, results in degradation of the body's proteins — muscle and so forth — in order to obtain the one that is needed. Unlike fat and starch, the human body does not store excess amino acids for later use—they must be present in the food every day. The essential ones include: Arginine, Histidine, Isoleucine, Leucine, lysine, Methionine, Phenylalanine, Trypophan, and Valine. Arginine, methionine and phenylalanine are considered essential for reasons not directly related to lack of synthesis. Arginine is synthesized by mammalian cells but at a rate that is insufficient to meet the growth needs of the body and the majority that is synthesized is cleaved to form urea.
References and Related links:
a) Amino Acid supplement Information
b) The Chemistry of Amino Acids