The Quality of Proteins

The nutritive value of a protein depends to an important degree on the relation of the amino aids in its molecule to those required for building new tissues. If the protein of the diet is seriously deficient in one or more of the essential amino acids, it is unlikely that nitrogen balance can be sustained, no matter how complete and excellent the food intake may be in all other respects.

It has long been known that proteins differ in quality according to the type of their amino acid content. They can be divided into two classes, those from animal sources - 1st class and those from vegetables - 2nd class.

However, certain mixtures of vegetable proteins are equivalent to 1st class animal proteins. Proteins are evaluated for their biological value on this basis. The protein of highest biological value for humans is egg protein, specifically that of the egg white.

Recommended Allowances For Protein

*RDI increases by 30gm/day during pregnancy and 20gm/day during lactation.

Protein/Energy Malnutrition - Most often seen together, particularly in underdeveloped countries, they are in fact two different conditions. Protein deficiency is known as KWASHIORKOR and energy deficiency as MARASMUS.

Protein excess - there are no benefits and there are risks associated with the over consumption of protein. Protein rich foods are often high fat foods that contribute to obesity and its accompanying health risks. High protein diets may facilitate the increased excretion of zinc from the tissues, also calcium from the bones. Extra protein increases the need for certain vitamins for its metabolism eg. vitamin B6, causing a deficiency of the vitamin. Over consumption of protein can also cause dehydration, because water is needed to help excrete the wasted nitrogen. While eating excess protein is clearly ill advised, taking protein or amino acids supplements is even more so, if used in excess.