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| Fig:-Proteins quality chart |
The efficiency or degree to which dietary proteins can be used for building parts of the human body is determined principally by the type and relative amounts of amino acids present in the particular protein molecule. The body has the ability to interconvert and make some of the amino acids. However, there are eight of the amino acids which cannot be put together in the body and, therefore, must be supplied by the food we eat. These eight are called ESSENTIAL amino acids. The nutritive value of proteins is determined by the presence in adequate amounts of the eight essential amino acids. Most animal proteins contain all of the essential amino acids in sufficient amounts. The protein of cereals, most beans, and vegetables may contain all the essential amino acids, but the amounts in these plant foods is less than ideal. The plant protein is, therefore, of lower nutritive value than that of the animal protein. Some of the plant proteins provide an excess of one or more of the essential amino acids while being short of some of the others. Thus, two plant proteins or one plant and one animal protein can complement each other. For example, black-eyed peas have a high lysine content (an essential amino acid) and when they are consumed along with wheat, which is low in lysine content, the combined protein is of improved nutritive value. Specific knowledge of the amino acid content of plant foods and complementary combinations can provide good quality protein. It should be pointed out that vegetable protein is less well digested and utilized than animal protein. If the main protein source is from vegetables, 65 grams per day is recommended as compared with 45 grams per day when animal products provide the primary protein source.
