Amino Acids

What they are and where to find them.

- By Lisa Turner

You’ve heard a lot about amino acids and how important they are for building muscle. But these building blocks of protein are responsible for many other critical systems and functions in the body, including neurotransmitter and hormone production, immune health, nervous system function, tissue repair, digestion, and reproduction.

When you eat foods that are high in protein, the body breaks them down into amino acids. Your body needs 20 different amino acids, which are categorized as essential, conditionally essential, or non-essential:

Essential amino acids are considered “essential” because your body can’t make them—you have to get them from your diet. There are nine of them: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

Non-essential amino acids are synthesized by the body, even if they’re not consumed in the diet. The eleven non-essential amino acids are alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.

Conditionally essential amino acids, also called “conditional amino acids,” include some non-essential amino acids whose synthesis may be limited under certain conditions, including serious illness, injury, surgery, or extreme trauma or stress. For instance, tyrosine is considered an essential amino acid for people with phenylketonuria (PKU), a condition in which the body can’t synthesize tyrosine. Other conditional amino acids include arginine, cysteine, glutamine, glycine, proline, and serine.