Scientists from the Department of Physiology at the University of Granada (UGR) have shown that caffeine (about 3 mg/kg, the equivalent of a strong coffee) taken half an hour before aerobic exercise significantly increases fat burning. They also found that if the workout is done in the afternoon, the effects of the caffeine are more pronounced than in the morning.
In their study, the researchers wanted to determine whether caffeine — one of the world's most commonly used ergogenic compounds to enhance sports performance — actually increases the oxidation or "burning" of fat during exercise. Despite the fact that its consumption in the form of supplements is very common, the scientific evidence for its beneficial claims is scarce.
“The recommendation to train on an empty stomach in the morning to increase fat oxidation is commonplace. However, this recommendation may lack a scientific basis, as it is not known whether this increase is due to morning exercise or the lack of food for an extended period of time,” explains the lead author of this study, Francisco José Amaro- Gahete of the UGR's Department of Physiology, from.
A total of 15 men (mean age 32) participated in the study, which involved taking exercise tests four times at seven-day intervals. Subjects took 3 mg/kg of caffeine or a placebo at 8 a.m. and 5 p.m. (each subject completed the tests in random order in all four conditions). Conditions prior to each exercise test (hours elapsed since the last meal, exercise, or consumption of stimulants) were strictly standardized and fat oxidation during exercise was calculated accordingly.
Maximum fat oxidation
“The results of our study showed that acute caffeine intake 30 minutes before performing an aerobic exercise test increased maximal fat oxidation during exercise, regardless of the time of day,” explains Francisco J. Amaro. The existence of a diurnal variation in fat oxidation during exercise was confirmed, with values higher in the afternoon than in the morning for equal hours of fasting.
These results also show that caffeine increases fat oxidation during morning exercise in a similar way to that observed without caffeine intake in the afternoon.
In summary, the findings of this study suggest that the combination of acute caffeine intake and aerobic exercise performed at moderate intensity in the afternoon provides the optimal scenario for people looking to increase their fat burning during exercise.
