Eating to Survive - Protein macro-nutrient

The main function of Protein is to aid in the growth and repair of the body. Aside from water, protein is the most abundant molecule in the body. Protein is found in all cells of the body and is the major structural component of all cells in the body, especially muscle. This also includes body organs, hair, and skin. Hormones and enzymes are also formed from amino acids in which help regulate metabolism, support the immune system and other body functions. Finally, protein is needed to form blood cells. Wikipedia