Protein is the chief component of all body tissues. We obtain proteins mainly from animal foods like milk products, meat, fish and egg. Pulses and nuts are also good sources of protein.
When you eat foods that contain protein, the digestive juices in your stomach and intestine go to work. They break down the protein in food into basic units, called amino acids. The amino acids then can be reused to make the proteins your body needs to maintain muscles, bones, blood, and body organs.
Proteins are sometimes described as long necklaces with differently shaped beads. Each bead is a small amino acid. These amino acids can join together to make thousands of different proteins. Scientists have found many different amino acids in protein, but 22 of them are very important to human health.
Of those 22 amino acids, your body can make 13 of them. Your body can’t make the other nine amino acids, but you can get them by eating protein-rich foods. They are called essential amino acids because it’s essential that you get them from the foods you eat.
Functions of Proteins:
For growth and maintenance: Proteins are required for growth and maintenance of the body tissues. More proteins are required by the body during periods of growth for they are needed to build up new tissues. Therefore, children need more proteins to grow normally. Pregnant mothers need more proteins for the growth of the fetus. Also, lactating mothers need extra proteins to help them in the secretion of milk.
Regulation of body processes: Many body processes are controlled by the presence of proteins in the body. For this, proteins present in the form of enzymes and hormones help to regulate a number of important body processes. Proteins also give resistance to the body to protect itself against infections.
Proteins as a source of energy: One gram of protein provides four kilocalories. But protein foods are expensive sources of energy. It is preferable to use proteins for growth and development only, by providing enough carbohydrates and fats in the diet so that proteins are spared.
Sources:
Animal protein sources: These include milk, egg, meat, fish and milk products like cheese, curd etc. Protein from animal sources is called complete, because it contains all nine of the essential amino acids.
Vegetable protein sources: Pulses like whole and split, soybeans, nuts and oil seeds like peanuts, almonds and cashew nuts etc., are rich sources of vegetable protein. Cereals like wheat and rice also provide some amount of protein. The proteins of these foodstuffs are incomplete because it lacks one or more of the essential amino acids. If any one of these foods is the only source of protein in the diet the protein is not completely used. However, a combination of these foods or their combination with any animal protein food improves their protein quality and they are used better. It is nutritionally better to use a mixture of cereals and pulses at a meal rather than using cereals or pulses alone. Similarly addition of even a small amount of milk, curd or other animal protein like meat, fish etc, improves utilization of plant proteins.