As a nutrient, protein performs many important functions. Protein is a part of every body cell and is needed to repair body cells as they wear out. Protein is also critical to the process of making new body tissue during times of growth - infancy, childhood, adolescence and pregnancy.
Protein also helps regulate body processes.
As enzymes and hormones, proteins are important to make various chemical reactions happen in the body. As antibodies, proteins protect you from disease-carrying bacteria and viruses. Protein is often referred to as a single nutrient. Yet, proteins in foods and in your body cells are made up of 20 amino acids. Nine of these amino acids are considered essential.