Researchers from the University of Granada's (UGR) Department of Physiology have demonstrated that consuming caffeine—about 3 mg/kg, equivalent to a strong cup of coffee—30 minutes before aerobic exercise significantly enhances fat burning. The effects are even more pronounced during afternoon workouts compared to mornings.
In this study, the team examined whether caffeine, a popular ergogenic aid for sports performance, truly boosts fat oxidation during exercise. While supplements are widely used, robust scientific evidence has been limited.
“The common advice to train fasted in the morning for better fat oxidation may not hold up scientifically,” says lead author Francisco José Amaro-Gahete, PhD, from UGR's Department of Physiology. “It's unclear if benefits stem from the time of day or prolonged fasting.”
Fifteen healthy men (average age 32) completed exercise tests four times, spaced seven days apart. They ingested 3 mg/kg caffeine or a placebo at 8 a.m. or 5 p.m., in randomized order. Pre-test conditions (fasting duration, prior exercise, stimulant avoidance) were strictly controlled, with fat oxidation measured precisely.
Maximum Fat Oxidation
“Our findings confirm that caffeine taken 30 minutes before aerobic exercise increases peak fat oxidation, regardless of time of day,” notes Amaro-Gahete. Diurnal variations exist, with higher fat oxidation in afternoons even after equal fasting. Caffeine in the morning mimics afternoon fat burning without it.
In essence, for optimal fat burning, combine 3 mg/kg caffeine with moderate-intensity aerobic exercise in the afternoon.
