Proteins: Sources
The sources of protein can be divided into two broad categories animal source and plant or vegetable source. Both of the sources are important source for supply of protein in our diet, depending on the cultural practice, religious belief, availability and locality.
Animal sources:
The important sources of animal protein include eggs, meat, fish, cheese and milk. The animal proteins contain all the essential amino acids and the quantity of these essential amino acids is adequate in animal protein. Essential amino acids have to be supplied in our diet as they can not be synthesized by our body.
The egg proteins are considered best among all the food proteins as egg protein has highest “biological value” and digestibility. For this quality the egg protein is used as “reference protein”.
Vegetable sources:
The rich sources of vegetable protein are pulses (lentils etc), cereals (rice, maize, wheat, millets etc), nuts, beans etc. In developing countries the vegetable proteins are the main source of protein in the diet. The vegetable source proteins are poor in essential amino acids. They are deficient in one or more essential amino acids. These are known as “limiting” amino acids. But combination of two or more vegetable protein compensates the deficiency of the essential amino acids. For example cereal protein (rice, wheat etc.) is deficient in lysine and threonine and pulse protein is deficient in metheonine. Here lysine, threonine and metheonine are the “limiting” amino acids. But when these two sources (here rice/wheat and pulse) are combined in the diet they compensates each other and make the whole of the protein “biologically complete”.