Creatine is a tripeptide (meaning a protein made up of 3 amino acids) that is made primarily of red meat. It is the main fuel of our ATP system - better known as the energy system responsible for explosive or high-intensity training. It is found primarily in red meat. Vegan, vegetarian and pescatarian diets have been shown to be low in creatine.
Most of the creatine's benefits come from transferring phosphate into the mitochondria in the form of phosphocreatine. The phosphocreatine supports ATP regeneration.