Creatine is an amino acid that occurs naturally in the body. Amino acids are the building blocks of protein, and protein makes up muscle and other tissues. High protein foods like beef, chicken and fish supply some creatine in the diet. Additional amounts may be beneficial in weight training, intense cardio workouts and other athletic activities. Although we tend to lose muscle mass as we age, creatine may also provide nutritive support to help maintain lean muscle in the elderly.