| Abstract | Background: Traditionally, many highly-trained athletes have consumed a high-carbohydrate diet (HCD) to enhance exercise performance. A more recent trend among some athletes is to consume a ketogenic diet (KD), a low-carbohydrate diet, for better exercise performance. It is not clear whether the traditional HCD results in better exercise performance compared to a KD in highly- trained athletes. Purpose: To compare the effects of a KD versus a HCD on exercise performance including time to complete a 30 km cycling time-trial, rating of perceived exertion (RPE), and substrate utilization or respiratory exchange ratio (RER). Methods: Five endurance trained male and female cyclists and triathletes, ages 18-70 years, were asked to consume a KD and a HCD, for 14 days each, in a randomized cross-over design. Measurements were taken at the beginning of the study while on the habitual diet (HD) and at the end of the KD and HCD conditions and included time to complete time-trial, RER, and RPE during a 30-km time trial. The effect of diet condition on time to complete the time-trial, RER, and RPE were assessed by repeated measures analysis. Results: Time required to complete a 30-km time-trial and RPE were not significantly different for participants between diet conditions. RER was significantly lower in the KD compared to HCD and HD conditions [F(2, 8) = 73.08, p = <.001, n2p = 0.948]. Conclusion: There was no difference in time to complete the time-trial or RPE by diet condition but a lower RER in the KD condition compared to the other conditions. Future studies with a larger sample size are needed. |
