Energy Drinks Alter Metabolism at Rest but not During Submaximal Exercise in College Age Males

Abstract

Energy drinks are widely available soft drinks which contain caffeine, vitamins, minerals, and other substances that are purported to increase feelings of energy. Energy drinks are popular among athletes and non-athletes alike for the purposes of enhancing vigor and exercise performance. Purpose. Evaluate the effects of energy drinks on energy expenditure and substrate metabolism at rest and during exercise. Methods. On four separate occasions a baseline measurement of resting metabolic rate (RMR) was 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 (16 oz) of 1 of 3 energy drinks (Red Bull, Rockstar, Monster) or a sugar free, caffeine free soft drink (placebo) and RMR was measured 1 hour later. The subjects then engaged in 15 minutes of treadmill exercise at 50% of V02max while oxygen consumption, heart rate, and respiratory exchange ratio (RER) were measured. Results. RMR was not changed by placebo, but was increased (P<0.05; means ± se) above baseline by 10 ± 2.5%, 15.3 ± 2.9%, and 15.0 ± 2.9% following Red Bull, Monster, and Rockstar (respectively) with no differences between energy drinks. RER was reduced below baseline (P<0.05) by 4.9 ± 1.5% in the placebo and was increased (P<0.05) above baseline by 12.8 ± 1.8%, 9.0 ± 1.3% and 9.6 ± 1.3% following Red Bull, Monster, and Rockstar (respectively) with no differences between energy drinks. Oxygen consumption and RER during submaximal exercise were not different between placebo, Red Bull, Monster or Rockstar. Heart rate at rest and during exercise was not altered due to energy drink or placebo intake. Conclusions. These data indicate that energy drink consumption increases energy expenditure and carbohydrate utilization at rest, but oxygen consumption and substrate metabolism during submaximal exercise are not changed. Furthermore, in healthy young men, consuming energy drinks does not alter heart rate at rest or during light intensity aerobic exercise. The present data also indicate that the magnitude of increase in RMR does not compensate for the calories provided by an energy drink. Therefore, energy drinks may contribute to obesity and do not appear to be ergogenic during short-term submaximal exercise.