Creatine is an amino acid (broken down protein) derived compound produced in the body that serves as the primary fuel source (ATP) for short duration, high-intensity activities such as sprinting and weightlifting. Creatine is stored primarily in muscle tissue, and it is used for rephosphorylating ADP into ATP.
This means that when our muscles use up our energy stores,creatine helps to replenish those stores in a very
rapid manner. Approximately 2 grams of creatine are found in individuals that do not supplement and maintain a diet including animal-based proteins. Those who do supplement can increase their body’s internal creatine pool
by 10 to 40% depending on diet and total lean muscle mass.
Natural sources of creatine include meat, eggs, fish, and milk but you would have to consume ~20 steaks/day in order to fully saturate creatine stores; while 5 grams a day of creatine monohydrate for 20 days will accomplish the same goal.