Amino acids

Amino acids are the breakdown products of proteins. They are divided into two groups, essential and non-essential:

Table 1. The Amino Acids

EssentialNon-essential
HistidineGlycine
IsoleucineGlutamate
LeucineAspartate
LysineProline
MethionineSerine
PhenylalanineAlanine
ThreonineTryptophan
TryptophanArginine
Valine 

Deficiency of any of the nine leads to wasting as proteins cannot be made without them. This usually only occurs with a very monotonous vegan diet, where the chief food is a plant that does not have one or more essential amino acid. A varied vegetarian diet solves the problem.

The other amino acids can be synthesised by the liver. The liver can also interchange two pairs: cysteine and methionine, and tyrosine and phenylalanine. This means a shortage of one can be made up from the other, so total as the total requirement is met.

Amino acid supplements are of no proven benefit over proteins containing the amino acids (but are much more expensive).