...protein is construction material for the human body like bricks are for a building. Body structures made from protein include skin, hair, nails, bones, connective tissue and of course skeletal muscle. Other proteins in your body include antibodies, enzymes, hormones such as insulin, and transporters such as hemoglobin. Next to water, protein is the most abundant substance in the body, making up approximately 15-20% of your weight. Of most interest to the bodybuilder is the fact that 60-70% of all protein in the body is located in the skeletal muscles. In order for muscle growth to occur, every day you must consume more protein than your body utilizes.