Caffeine Increases Rate of Fat Oxidation During Exercise in Healthy Young Males and Females

Caffeine is a small amphiphilic molecule influencing many physiological processes. Caffeine has both ergogenic and metabolic effects, but its impact on fat metabolism during exercise remains controversial. Therefore, the aim of the present study was to carefully investigate the effect of caffeine on fat oxidation. Twelve participants (8 males and 4 females) were included in the study with a double-blind, randomized, placebo-controlled cross-over design. Caffeine (3 mg/kg) or placebo were provided 60 min before participants completed the fat oxidation test. Fat oxidation was calculated from respiratory gas exchange at intensities between 30% and 80% of maximal oxygen uptake. Maximal fat oxidation was 16% higher with caffeine than placebo. Maximal fat oxidation was obtained at 40% of VO 2max , but caffeine increased the rate of fat oxidation up to 70% of VO 2max . Plasma FFA and blood lactate were higher with caffeine than placebo. The elevated fat oxidation with caffeine in conjunction with higher plasma lactate suggests that the higher fat availability may be related to the reduced carbohydrate oxidation (Randle cycle). In conclusion, moderate caffeine intake increased plasma FFA and rate of fat oxidation at low and moderate intensity cycling.