Caffeine increases maximal fat oxidation during a graded exercise test: is there a diurnal variation?
Mauricio Ramírez-Maldonado1, Lucas Jurado-Fasoli2,1, Juan Del Coso3
1PROFITH "PROmoting FITness and Health Through Physical Activity" Research Group, Department of Physical Education and Sport, Faculty of Sport Sciences, University of Granada, Granada, Spain.
Journal of the International Society of Sports Nutrition
|January 8, 2021
Summary
Caffeine intake boosts maximal fat oxidation rate (MFO) and aerobic capacity in active men, regardless of the time of day. This study confirms diurnal variations in MFO, enhanced by caffeine.
Area of Science:
- Exercise Physiology
- Nutritional Biochemistry
- Sports Science
Background:
- Maximal fat oxidation rate (MFO) and aerobic capacity exhibit diurnal variations, being lower in the morning than in the afternoon.
- Caffeine is known to increase MFO and aerobic capacity.
Purpose of the Study:
- To investigate the effect of caffeine on the diurnal variation of MFO during graded exercise in active men.
- To determine if caffeine intake influences maximal oxygen uptake (VO2max) and the exercise intensity eliciting MFO (Fatmax) throughout the day.
Main Methods:
- A triple-blind, placebo-controlled, crossover study involving 15 caffeine-naïve active men.
- Participants completed graded exercise tests after ingesting 3 mg/kg of caffeine or placebo at 8 am and 5 pm.
- MFO, VO2max, and Fatmax were measured using indirect calorimetry.
Main Results:
- MFO, Fatmax, and VO2max were significantly higher in the afternoon compared to the morning (P < 0.05).
- Caffeine ingestion significantly increased MFO by 10.7% in the morning and 29.0% in the afternoon (P < 0.001).
- Caffeine also elevated Fatmax by 11.1% in the morning and 13.1% in the afternoon (P < 0.008).
Conclusions:
- The study confirms diurnal variations in whole-body fat oxidation during graded exercise in active men.
- Acute caffeine ingestion enhances MFO, Fatmax, and VO2max, independent of the time of day.
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