J Appl Physiol 2002 Aug 16; [epub ahead of print]

Creatine supplementation influences substrate utilization at rest.

Huso ME, Hampl JS, Johnston CS, Swan PD.

Department of Nutrition, Arizona State University, Mesa, AZ, USA.

The influence of creatine supplementation on substrate utilization during rest was investigated using a double-blind crossover design. Ten active men participated in 12 weeks of weight training and were given creatine and placebo (20 g/d for 4 d, then 2 g/d for 17 d) in two trials separated by a 4-week washout. Body composition, substrate utilization, and strength were assessed following week 2, 5, 9 and 12. Maximal isometric contraction (1-RM) leg press increased significantly (P < 0.05) following both treatments but 1-RM bench press was increased (33 kg +/- 8, P < 0.05) only following creatine. Total body mass increased (1.6 kg +/- 0.5, P < 0.05) after creatine but not after placebo. Significant (P < 0.05) increases in fat-free mass were found following both creatine (1.9 kg +/- 0.8) and placebo (2.2 kg +/- 0.7) supplementation. Fat mass did not change significantly with creatine, but decreased after the placebo trial (-2.4 kg +/- 0.8, P < 0.05). Carbohydrate oxidation was increased by creatine (8.9% +/- 4.0, P < 0.05), while there was a trend for increased RER after creatine supplementation (0.03 +/- 0.01, P = 0.07). Changes in substrate oxidation may influence the inhibition of fat mass loss associated with creatine following weight training.

Note: RER, or Respiratory Exchange Ratio, is a measure of how much fat vs. how much glucose is being used for fuel. The higher the RER, the more glucose/less fat there is being burned.