Creatine is a compound that's involved in the production of energy in the body, in the form of adenosine triphosphate (ATP). Made in the liver, approximately 95% of the body's creatine ends up being stored in skeletal muscles and the remaining 5% is found in the brain, heart and testes. Once it's used, creatine is converted to a waste product called creatinine and excreted in urine.
Creatine is found in small amounts in red meat and fish. However, much of it is destroyed by cooking. It's also made naturally in the body from L-arginine, L-glycine and L-methionine, amino acids that are principally found in animal protein. Insulin is needed for creatine to enter muscles, so consuming carbohydrates with creatine may increase the amount of creatine available to muscles.
Creatine supplements are available in capsules or as a powder at health food stores, some drug stores and online. One of the most popular forms of creatine is creatine monohydrate.