How to improve the Quality of Protein in the Diet?
Since the net protein utilization (NPU) values of milk or egg proteins are higher than those of proteins of average diets consumed in different countries, a correction has to be made for this variation in the NPU of dietary proteins, This is shown herewith:
Dietary protein requirements (g) = Safe level of intake of egg or milk proteins x NPU of egg or milk proteins / NPU of dietary proteins
For example, if the NPU of the dietary proteins is 45 and egg protein is 90, the correction factor will be 2. In other words, the amount of this dietary protein needed to satisfy the requirements of a given population group will be twice as high as that, of egg or milk protein. The next thing that might come to your mind is regarding the protein quality of the Indian diets. An average diet as consumed in different parts of the country consists chiefly of vegetable source of protein. The amount of animal protein depends on the diet habits, with only milk providing a source of animal protein in vegetarian diets to varying amounts of meat and flesh in the non .vegetarian diets. The question of whether the protein quality of our pre-dominantly vegetarian diets is adequate and what are the ways in which the quality of protein in our diets can be improved has been addressed through a number of studies. Habitually, Indian diets are cereal-based diets, limiting in lysine, an essential amino acid critical for growth and development in children. The term limiting is used to describe that indispensable amino acid which is present in the lowest quantity in the food, in comparison with the same amino acid in a reference protein such as egg or milk, the quantity of the amino acid expressed in terms of per g nitrogen. Further, the diet is predominantly vegetable-based, and foods of animal origin do not usually find a place because of their high cost. A large percentage of people are vegetarian and their diets include pulses, vegetables, cereals and grain products. These plant foods tend to have too little of one or more indispensable amino acids (i.e. lysine, threonine, tryptophan or methionine, particularly in legumes).
In other words, individual plant foods such as cereal alone or pulses alone tend to be relatively deficient in one or more essential amino acids and thus exclusive consumption of single plant foods such as chiefly rice or wheat would result in deficiency of an essential amino acid and if this consumption pattern is continued over a long period of time, it can result in protein deficiency. However, a combination of plant foods, such as cereal-pulse-vegetable based diets are fully capable of meeting protein needs, when consumed in amounts that satisfy energy needs. Fortunately, for us, the amino acid deficient in cereals, namely lysine is present in ample quantities in pulses and green leafy vegetables. Similarly, the essential amino acid methionine which is relatively low in pulse, is present in larger quantities in cereals. Thus, the different sources of vegetable proteins complement each other in terms of the amino acids they provide. Therefore, if we ensure that diet at every meal is a combination of cereals, pulses, and vegetables with nuts and milk contributing wherever one can afford, it will take care of the protein requirements. In this context, when we consider the Indian cuisine we notice, North and West Indian meals consist of chapattis or rotis and rice as staples, eaten with a wide variety of side dishes like dals, curries, yoghurt, chutney and achars. South Indian dishes are mostly rice-based, sambhar, rasam and vegetables being important side dishes. The pulses/legumes, included in the diet, with their high content of lysine but low content of methionine, complement the grains (cereals), which are more than adequate in methionine and cystiene but limiting in lysine. Such cereal-pulse combination diets when consumed help the body receive all the indispensable amino acids. Hence, there is no need to worry about protein if we are eating a varied vegetarian diet! It is easy to get protein from lentils, dal, beans, curd, rice, soy milk, and cereals when eaten in combination so that their amino acid patterns become complementary. The inclusion of pulses in cereal-millet-based diets is critical not only in increasing the protein content, but also in improving the nutritional quality of the protein.