Protein is essential to the human body for growth and repair of tissue.
Beyond making muscle, protein helps athletes to maintain blood, to keep hormones working and to fight off disease by enriching the immune system. Protein is made up of chains of amino acids, some of which the body cannot manufacture. Athletes who get too little protein may find that their hair falls out easily, and females may develop amenorrhea. A high-carbohydrate diet that is low in protein can still cause fatigue and poor performance. Other athletes may overdo protein intake at the expense of a balanced diet, or rely on amino acid supplements of questionable value to increase protein intake that basic diet improvements could provide.