Energy drinks are widely available and popular among athletes and non-athletes. However, the effects of energy drinks on resting and exercise energy expenditure and metabolism remain largely unknown. On four separate occasions, baseline measurements of resting metabolic rate (RMR) and Respiratory Exchange Ratio (RER) were obtained in ten healthy males (21.4 ± 1.6 y, 77.60± 7.5 kg, 180.0 ± 7.1 cm). Then, in a randomly assigned cross-over design, the subjects consumed 473 ml of one of three commercially available energy drinks or a placebo and then RMR and RER were measured 1 hour later. The subjects then engaged in 15 minutes of treadmill exercise at 50% of V02max, during which RER and oxygen consumption (VO2) were measured. RMR was not changed by placebo, but increased (P<0.05, means ± se) above baseline by 10 ± 2.5%, 15.0 ± 2.9%, and 15.3 ± 2.9%, following Energy Drink One, Energy Drink Two, and Energy Drink Three (respectively) with no differences between energy drinks. RER was reduced below baseline (P<0.05) by 4.9 ± 1.5% in the placebo and increased (P<0.05) above baseline by 12.8 ± 1.8%, 9.6 ± 1.3%, and 9.0 ± 1.3% following Energy Drink One, Energy Drink Two, and Energy Drink Three (respectively) with no differences between energy drinks. Oxygen consumption and RER during submaximal exercise were not different between placebo, Energy Drink One, Energy Drink Two, or Energy Drink Three. These data indicate that energy drink consumption increases RMR and carbohydrate use at rest, but metabolism during submaximal exercise remains unchanged.