As with essential fatty acids (see Chapter 10 ‘Lipids’, p. 78) not all amino acids can be synthesized by the body; some have to be taken in with food. They are generally considered essential in children as their metabolism is not mature enough to synthesize them.

Of the 20 standard amino acids that are encoded by DNA (there are considerably more amino acids than this but they are outside the scope of this book), 10 cannot be manufactured by the human body (essential amino acids); the remaining 10 can be synthesized and are therefore known as the non-essential amino acids. Plants contain all 20 amino acids. Their general structure is seen in Figure 11.2.

Figure 11.2 The general primary structure of amino acids.

The essential amino acids (Figure 11.1) are:

Figure 11.1 The 20 common amino acids.

The non-essential amino acids are: