Carbohydrate mouth-rinsing does not rescue simulated time trial performance in trained endurance cyclists following a 5-day ketogenic diet

Abstract

Background: Carbohydrate mouth rinsing (CHO-MR) during periods of fasting or low muscle glycogen availability could provide a more pronounced ergogenic effect compared to fed and high muscle glycogen conditions. However, there is little evidence investigating the efficacy of CHO-MR during periods of low muscle glycogen induced by ketogenic diets. Therefore, this study aimed to investigate the impact of CHO-MR vs. a placebo (PLA-MR) on cycling time trial performance in trained endurance cyclists following their habitual diet (HD) or a 5-day ketogenic diet (KD). Methods: Eight participants completed baseline testing and four trial conditions. For each trial, participants adhered to either their HD or a KD for 5 consecutive days. During the first 4 days of each dietary phase, they tracked daily nutrition; additionally, they recorded morning fasting blood glucose and β-hydroxybutyrate (βHB) levels for the 4 days preceding and the morning of each trial. Each trial comprised a 33.6 km simulated time trial in which rinsing was performed for ten seconds at 7 km intervals. Results: The 5-day KD significantly increased the time to completion (TTC) compared to HD (p