Protein is a class of complex nitrogenous compounds composed of amono acids.
Human proteins are formed in the body from amino acids derived from the digestion of protein-containing foods or from amino acids manufactured by the body.
Proteins are formed from about 20 different amino acids, synthesize most of these. A total of eight essential amino acids cannot be made by the body, and so they must be obtained from the diet. These essential amino acids occur in a wide variety of foods, including grains, seeds, and vegetables, fish, and dairy products.
Hemoglobin, a complex protein, is responsible for carrying oxygen to all cells. Enzymes are also complex proteins and are necessary for metabolism.