Medium-chain triglycerides with maltodextrin increase fat oxidation during moderate-intensity exercise and extend the duration of subsequent high-intensity exercise

Medium-chain triglycerides (MCT) are useful for increasing fat utilization during exercise. The highest rate of fat oxidation during submaximal exercise tends to precede the lactate threshold in untrained adults. In our previous study, blood lactate concentration was more than 4 mmol/L (onset of blood lactate) in recreational athletes during exercise at a workload corresponding to 60% peak O₂ uptake (V o₂), which was below ventilation threshold. In the present study, we investigated the effect of 2 week of ingestion of food containing 6 g MCT on substrate oxidation during moderate-intensity (50% peak V o₂) exercise and high-intensity (70% peak V o₂) exercise in recreational athletes. For comparison, two experimental trials were conducted after participants had been administered isoenergic test foods (MCT-supplemented food with mainly maltodextrin-containing carbohydrate (MCT + CHO) or CHO) for 2 weeks, with a washout period between trials. Participants were instructed to perform cycle ergometer exercise at a workload corresponding to 50% peak V o₂ for 40 min followed by a workload corresponding to 70% peak V o₂ until exhaustion. Fat oxidation was significantly increased in the MCT + CHO trial (13.3 ± 2.7 g/40 min, mean ± SD, p < 0.05) during moderate-intensity exercise and the duration was extended significantly (23.5 ± 19.4 min, p < 0.05) during subsequent high-intensity exercise, compared with that observed in the CHO trial (fat oxidation; 11.7 ± 2.8 g/40 min, duration; 17.6 ± 16.1 min). In conclusion, continuous ingestion of 6 g MCT with maltodextrin could increase fat oxidation during moderate-intensity exercise and extend the duration of subsequent high-intensity exercise in recreational athletes, compared with the ingestion of isoenergic maltodextrin alone.