Commonly referred to as ‘the building blocks of protein’, amino acids are needed to make almost all components of the body including enzymes, blood corpuscles, hormones, antibodies, hair, skin, bone and tissues.
Amino acids are generally linked together by peptide bonds, to form peptides. When ten or more are linked, these are known as polypeptides. Very large polypeptides are known as proteins. Amino acids are often classified according to whether they are ‘essential’ or ‘non-essential’. This is a potentially misleading description since it is sometimes assumed to mean that most amino acids do not play an essential role in the body. In fact the term ‘essential’ does not refer to the role of the amino acids but to the body’s ability to synthesize them. ‘Essential’ amino acids are those which the body is incapable of synthesizing and which must, therefore, be obtained from the diet. Although equally important, amino acids such as taurine, carnitine and tyrosine can, at least in healthy individuals, be synthesized from other amino acids and are therefore described as ‘non-essential’.
Some authorities have made statements that amino acid supplementation is valueless because most people in the western world already eat too much protein. However this fails to take account of individual biochemistry and possible errors of metabolism. Some people may be less capable than others of synthesizing ‘non-essential’ amino acids and would therefore benefit from supplementation, especially if they do not regularly consume animal products in their diet.
Amino acids can be divided into a number of categories according to their structure and functions:
- Amino acids with important metabolites: lysine, carnitine, histidine
- Aromatic amino acids: phenylalanine, tyrosine and tryptophan
- Branched chain amino acids: leucine, isoleucine, valine
- Glutamate amino acids: glutamic acid, GABA, glutamine, proline, hydroxyproline, aspartic acid, asparagine
- Sulphur amino acids: cysteine, glutathione, taurine, methionine, homocysteine
- Threonine amino acids: threonine, glycine, serine, alanine
- Urea cycle amino acids: arginine, citrulline, ornithine
Glucogenic amino acids are those which, after losing their amino group, give rise to metabolic intermediate substances which form glucose. These are: alanine, arginine, aspartic acid, cysteine, glutamic acid, glycine, histidine, hydroxyproline, methionine, proline, serine, threonine and valine.
Amino acids can occur in two isomer forms known as the ‘D’ and ‘L’ forms. This is why you will often see them described as L-tryptophan or L-tyrosine for instance. The ‘D’ form of amino acids is not usually found in nature and, with the exception of D-phenylalanine, is not normally utilizable by the human body.
The so-called essential amino acids
Information compiled by Linda Lazarides
Naturopathic Nutritionist, Author, Educator