Creatine is an amino acid that forms creatine phosphate in the body. Creatine intake generally comes from eating meat and fish, although it can be synthesized in the body from other amino acids. Creatine in the form of creatine monohydrate, creatine ethyl ester and/or tri-creatine citrate, has become a popular nutritional supplement because it has been shown to improve performance of high intensity exercise.
All energy in the body comes from the dephosphorylation of adenosine tri-phosphate (ATP). When a phosphate is removed from ATP, adenosine diphosphated (ADP) remains and energy is released. That energy allows the body to do work. Unfortunately we have a finite pool of ATP, and we cannot store extra amounts of it. Therefore, our bodies try to replenish ATP quickly as we break it down. The more ATP we can replenish, the more energy we can create, and the more work we can do.
How Creatine Helps Create ATP
We can replenish ATP in several different ways, all of which have unique characteristics regarding at what speed and for how long ATP is created. The first ATP-replenishment system to act when energy is needed is the creatine phosphate (CrP) system. In this system CrP combines with the ADP that remains from ATP breakdown, donating its phosphate to create ATP. This system creates ATP at a faster rate than any other energy system. However, as with ATP, the body has a small and finite store of CrP. Ingesting supplemental creatine can boost the creatine phosphate system, providing for enhanced replenishing of ATP during short duration, high intensity activities like sprinting or weight training.
Creatine and Weight Gain
Certainly creatine can cause weight gain due to muscle hypertrophy. If one is able to weight-train at a higher intensity and/or volume due to the ergogenic influence of creatine, enhanced muscle strength and size logically follow. The question, however, is about non-muscle weight gain, the possibility that creatine can make you gain weight in other ways. The short answer is yes. An early study of creatine supplementation by Ziegenfuss, et al., first made the case that creatine ingestion causes fluid retention. They postulated that as creatine is taken into the cells, it is accompanied by water. This results in a higher amount of intracellular water and total body water, which typically shows up on the scale as 1 to 2 kilograms of weight gain.
Implications of Creatine-Induced Water Weight Gain
Lopez, et al., recently published a meta-analysis of several studies that examined, among other things, the body mass change that may take place when taking supplemental creatine. They found in nine of ten studies reviewed that an increase in body mass as a result of creatine supplementation occurred and that generally these increases were the result of intracellular water gains. Obviously, these gains could be detrimental for a fighter or a jockey trying to make weight. However, otherwise they appear harmless and reversible. Lopez's paper made it clear that this additional intracellular water does not hamper thermoregulation or otherwise make creatine users more susceptible to cramps, heat exhaustion or other heat illnesses.
Creatine supplementation does cause weight gain both long-term, by increasing muscle size with improved training, and short-term by increasing the amount of water stored in muscle cells. However, with the termination of creatine supplementation, total body water shortly returns to normal, while muscle gains may be much longer lasting.