During Biochemistry practical examination of our B.Pharm Part 1 Examination at Jadavpur University, one of our class-mates was asked in the viva-voce: “Why do we prefer animal proteins over vegetable proteins as food? She promptly replied: “Because they are tastier than vegetable proteins,” much to the amusement of the external examiner,
The correct answer is related to the fact that all naturally occurring proteins are made of 20 amino acids. We require all of them to build body proteins. Among them, 10 amino acids are synthesized in our body, 2 are synthesized but used up in some other reactions (so not available for protein synthesis) and 8 are not synthesized at all. Hence we require these 2+8=10 amino acids as supplements in the food. They are called essential amino acids. The content of the essential amino acids is higher in animal proteins than in vegetable proteins. That is why we prefer animal proteins to vegetable proteins in our diet. Definitely chicken, mutton and egg are tastier than dal or soya bean. But their food value hinges on the fact that they are rich source of the essential amino acids. Hence, they are dubbed as first class proteins while the proteins obtained from plants are called second class proteins.
Benefits are most often associated with some problems. In this case also the high food value of the first class proteins is accompanied with a health risk. Methionine is one of the 10 essential amino acids. When we take animal proteins, they are digested to generate a lot of essential amino acids including methionine. It is further metabolized to produce a compound called homocysteine. Accumulating evidences strongly indicate that increased blood level of homocysteine is associated with increased risk of some vascular diseases (e.g, heart attack and cerebral stroke). The exact role of homocysteine in triggering the deadly diseases is yet to be elucidated but scientists are sure about its association with the ailments. A blood level above 140-150 microgram of homocysteine per deciliter of blood in adults is considered “high” by the doctors.
So what should we do to avoid the danger? Should we avoid the first class proteins or the proteins as a whole in our diet ? Definitely not. That will invite many other health problems. Homocysteine is metabolized with the help of some members of the Vitamin B group. We should supplement them through vegetables and fruits. Thus we could help metabolize homocysteine and maintain its level within a safe range in the blood. So we should opt for a balanced diet (food containing protein, carbohydrate, fat, vitamins, minerals in the desired amounts) instead of overemphasizing on a high protein diet. A healthy food habit will help us keep the doctors at bay. The widely held notion that only high protein foods are nutritious and vegetables are junk is not only wrong but it may ultimately lead to serious health hazards. When we do not get sufficient amount of vegetables and fruits with a non-vegetarian meal, we can resort to vitamin supplements. But we should try our best to acquire vitamins from their natural sources.