Every cell in your body is built from protein. It makes up the essential building blocks of your muscle, bone, cartilage, skin, blood, and lymph. Your hair and fingernails consist of fibers of a protein called keratin. Collagen is a protein which strengthens your skin, blood vessels, bones, teeth and provides glue that binds the cells in various organs and tissues. Your mucles are made up of fibers of protein called myosin and actin. Protein also helps regulate the balance of water and acids in your body.