Protein plays a role in virtually everything that goes on in your body. Protein in your blood transports oxygen throughout your body. It builds and repairs tissue (including muscle tissue) and makes enzymes, hormones, and other body chemicals. Protein is a fundamental building block of bones, muscle, cartilage, organs, skin, blood, hair, and nails.

The antibodies our bodies use to ward off disease and infection are made of protein, as are the enzymes that read the genetic information in our DNA to make new molecules. Messenger proteins transmit signals between cells, tissue, and organs, and transport proteins carry atoms and small molecules throughout the body.