Effect of caffeine intake on fat oxidation rate during exercise: is there a dose–response effect?

Purpose The effect of caffeine to enhance fat utilisation as fuel for submaximal aerobic exercise is well established. However, it is unknown whether this effect is dose dependent. The aim of this study was to investigate the effect of 3 and 6 mg of caffeine per kg of body mass (mg/kg) on whole-body substrate oxidation during an incremental cycling exercise test. Methods In a double-blind, randomised, and counterbalanced experiment, 18 recreationally active males (maximal oxygen uptake [VO 2max ] = 56.7 ± 8.2 mL/kg/min) performed three experimental trials after ingesting either 3 mg/kg of caffeine, 6 mg/kg of caffeine or a placebo (cellulose). The trials consisted of an incremental exercise test on a cycle ergometer with 3-min stages at workloads from 30 to 80% of VO 2max . Energy expenditure, fat oxidation rate, and carbohydrate oxidation rate were continuously measured by indirect calorimetry. Results During exercise, there was significant effect of substance ( F = 7.969; P = 0.004) on fat oxidation rate. In comparison to the placebo, the rate of fat oxidation was higher with 3 mg/kg of caffeine at 30, 40, 50 and 70% of VO 2max [all P