Two thirds of the average intake is obtained from animal sources, ie meat , fish , eggs and dairy foods. A further quarter is obtained from cereal products, and most of the remainder from nuts and pulses. Cereals, nuts and pulses are the principle sources of protein for people on a vegan diet. The Dietary and Nutritional Survey of British Adults . The building blocks of protein are amino acids.
Amino acids are compounds containing carbon, hydrogen, oxygen, nitrogen, and occasionally sulphur.
All amino acids have an acid group and an amino group attached to a carbon atom. Figure 2 shows the general structure of an amino acid. The rest of the amino acid is represented by R in Fig 2 and is different for every amino acid. There are about twenty different amino acids commonly found in plant and animal proteins. The amino group of one amino acid can link with the acid group of another amino acid to form a chain of amino acids.