Amino acids are critical to life, and have a variety of roles in metabolism. One particularly important function is as the building blocks of proteins, which are linear chains of amino acids. Every protein is chemically defined by this primary structure, its unique sequence of amino acid residues, which in turn define the three-dimensional structure of the protein. Just as the letters of the alphabet can be combined to form an almost endless variety of words, amino acids can be linked together in varying sequences to form a vast variety of proteins. Due to this central role in biochemistry, amino acids are very important in nutrition.

A total of 20 different kinds of amino acids form proteins. The kinds of amino acids determine the shape of the proteins formed. Commonly recognized amino acids include glutamine, glycine, phenylalanine, tryptophan, and valine. Three of those — phenylalanine, tryptophan, and valine — are essential amino acids for humans; the others are isoleucine, leucine, lysine, methionine, and threonine. The essential amino acids cannot be synthesized by the body; instead, they must be ingested through food.

One of the best-known essential amino acids is tryptophan, which performs several critical functions for people. Tryptophan helps induce normal sleep; helps reduce anxiety, depression, and artery spasm risk; and helps produce a stronger immune system. Tryptophan is perhaps most well-known for its role in producing serotonin, which is what gets all the press at Christmas time for putting you to sleep after the big Christmas lunch.

Amino acids make up 75% of the human body. They are essential to nearly every bodily function. Every chemical reaction that takes place in your body depends on amino acids and the proteins that they build.

The essential amino acids must be ingested every day. Failure to get enough of even one of the 10 essential amino acids can result in protein degradation. The human body simply does not store amino acids for later use, as it does with fats and starches. You can find amino acids many places in nature. In fact, more than 300 have been found in the natural world, from such diverse sources as microorganisms and meteorites.