He pointed to data sets in Mayo Clinic Proceedings that found resistance training reduced the risk of developing metabolic syndrome or hypercholesterolemia. “If you build muscle, even if you’re not aerobically active, you burn more energy because you have more muscle. This also helps prevent obesity and provide long-term benefits on various health outcomes.”
^ Spillane M, Schoch R, Cooke M, Harvey T, Greenwood M, Kreider R, Willoughby DS (February 2009). "The effects of creatine ethyl ester supplementation combined with heavy resistance training on body composition, muscle performance, and serum and muscle creatine levels". Journal of the International Society of Sports Nutrition. 6 (1): 6. doi:10.1186/1550-2783-6-6. PMC 2649889. PMID 19228401.
Weight gain might be the most common side effect. “Creatine can cause your body to hold on to water by pulling fluid into your cells via osmosis,” says Bates. “It doesn't necessarily cause you to gain weight as fat, but it can increase edema, or water weight.” Also, muscle is denser than fat, so in some cases building muscle can increase body weight overall (even if you’re simultaneously burning fat).
When assessing the antioxidant effects of creatine, it does not appear to sequester superoxide and may not be a direct antioxidant. Additionally, creatine failed to protect neurons from H2O2 incubation to induce cell death via pro-oxidative means. These results are in contrast to previously recorded results suggesting creatine acts as a direct anti-oxidant.
Kornblum, C., Schroder, R., Muller, K., Vorgerd, M., Eggers, J., Bogdanow, M., Papassotiropoulos, A., Fabian, K., Klockgether, T., and Zange, J. Creatine has no beneficial effect on skeletal muscle energy metabolism in patients with single mitochondrial DNA deletions: a placebo-controlled, double-blind 31P-MRS crossover study. Eur J Neurol 2005;12(4):300-309. View abstract.
Creatine is marketed as "nature's muscle builder" and "the most legitimate sports supplement around." Professional and amateur athletes alike are gobbling up this alleged ergogenic aid, hoping to increase their strength and performance. Creatine supplementation is claimed to increase muscle power by playing a role in the transfer of energy to help the muscle contract. Supplement labels state that "creatine is converted to phosphocreatine, which is important for short energy bursts such as sprinting and weight lifting" and that "depletion of phosphocreatine can result in muscle fatigue and fading muscle power." Claims are also made that supplementation increases muscle body mass.
Increasing creatine levels in skeletal muscle to 687% of baseline (0.5mM creatine, thought to be equivalent to 5g creatine) doesn’t seem to per se increase glucose uptake, but increases glucose oxidation (140% of baseline) which is due to a two-fold increase in the activity of α1 and α2 subunits of AMPK, a potency comparable to 1mM of the reference drug AICAR. Glucose uptake associated with AMPK has indeed been noted in diabetic people who are undergoing physical exercise and in contracting skeletal muscle cells, but according to rat and in vitro studies of cells not being contracted, this is not a per se effect of non-exercising tissue but an augmentation of exercise-induced glucose uptake.
Creatine is a hydrophilic polar molecule that consists of a negatively charged carboxyl group and a positively charged functional group . The hydrophilic nature of creatine limits its bioavailability . In an attempt to increase creatines bioavailability creatine has been esterified to reduce the hydrophilicity; this product is known as creatine ethyl ester. Manufacturers of creatine ethyl ester promote their product as being able to by-pass the creatine transporter due to improved sarcolemmal permeability toward creatine . Spillane et al  analyzed the effects of a 5 days loading protocol (0.30 g/kg lean mass) followed by a 42 days maintenance phase (0.075 g/kg lean mass) of CM or ethyl ester both combined with a resistance training program in 30 novice males with no previous resistance training experience. The results of this study  showed that ethyl ester was not as effective as CM to enhance serum and muscle creatine stores. Furthermore creatine ethyl ester offered no additional benefit for improving body composition, muscle mass, strength, and power. This research did not support the claims of the creatine ethyl ester manufacturers.