Effects Of Caffeine Intake On Substrate Oxidation With Aerobic Exercise In Oral Contraceptive Users

PURPOSE: Oral contraceptive (OC) use has been associated with increased blood lipid levels, highlighting the need for effective lipid management strategies. Caffeine, which affects substrate oxidation during exercise and increases fat oxidation, may serve as a beneficial approach. Additionally, OCs delay the metabolism of caffeine, thereby prolonging its effects. However, the effect of caffeine intake on substrate oxidation in individuals using OC with aerobic exercise is unclear. Therefore, we aimed to investigate the effect of caffeine intake on substrate oxidation in individuals using OC with aerobic exercise. METHODS: This double-blind, randomized, crossover study involved 13 women (age; 24.5 ± 2.2 years) using OC. Participants completed two laboratory-based trials, consuming either caffeinated coffee (CAF, caffeine; 5 mg/kg) or decaffeinated coffee (CON) 60 min before exercise. Each trial consisted of three 10-min bouts of exercise on a cycle ergometer at 40% peak oxygen uptake. Serum caffeine concentrations were measured before intake, pre-exercise (pre), post-exercise (post), and at 30-, 60-, and 90-min post-exercise (post30, post60, and post90, respectively). Oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured before intake, pre, during exercise, post30, post60 and post90. Fat (FOX) and carbohydrate (COX) oxidation were calculated using indirect calorimetry. RESULTS: All participants were using low-dose OCs containing 20-35 μg of ethinyl estradiol (EE). Serum caffeine levels in the CAF were significantly higher than in the CON pre, post, post30, post60, and post90 (p < 0.01). Total FOX and COX during and after exercise were not significantly different in both trials (p > 0.05). However, the change in total FOX after exercise were significantly higher in the CAF than in the CON (CAF, 0.06 ± 0.06, CON, 0.03 ± 0.05 g; p < 0.05). Conversely, the change in total COX after exercise was significantly lower in the CAF than in the CON (CAF, -0.12 ± 0.11, CON, -0.06 ± 0.12 g; p < 0.05). No significant correlation was found between the change in total FOX after exercise and EE dose in either trial (all p > 0.05). CONCLUSION: The findings of this study suggest that caffeine intake before exercise may enhance fat oxidation after aerobic exercise in OC users, regardless of the EE dose.