Amino acids are the building blocks of protein. Growth, repair, and maintenance of all cells are dependent upon them. Next to water, protein makes up the greatest portion of our body weight. Twenty amino acids are needed to build the various proteins essential for the growth, repair and maintenance of bodily tissues. Eleven of these amino acids can be manufactured by the body and are referred to as non-essential amino acids, while the other nine are called essential amino acids and must come from the diet. The classification of an amino acid as essential or non-essential does not reflect its importance, because all twenty amino acids are necessary for health.

Essential amino acids include isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Another amino acid, histidine, is considered semi-essential because the body does not always require dietary sources of it. The non-essential amino acids are arginine, alanine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, proline, serine and tyrosine. Other amino acids, such as carnitine, are used by the body in ways other than protein-building and are often used therapeutically.