A good protein diet should contain one or more of the animal proteins or a mixture of plant proteins. These is because dietary proteins are classified into first and second class proteins depending on their content of essential amino acids. First class proteins contain all the essential amino acids-must be obtained from diet since body don’t synthesis them. They include nearly all proteins of animal origin, e.g. beef, milk and egg proteins as well as some plant proteins such as soya bean protein. Second class proteins are deficient in one or more of the essential amino acids.
They include most proteins of plant origin especially those from grains. Beans and other legumes for example are rich in lysine but deficient in methionine which are both vital for specific body functions. So, a good protein diet should contain one or more of the animal proteins or a mixture of plant proteins.