High rates of fat oxidation are maintained after the sleep low approach despite delayed carbohydrate feeding during exercise

Training with low carbohydrate availability enhances endurance training adaptations but training volume may be compromised. We explored whole-body metabolism and performance with delayed carbohydrate feeding during exercise undertaken following acute sleep-low training. We hypothesised this strategy would not suppress fat oxidation and would maintain exercise performance. The study involved three experimental trials and included 9 men and 1 woman (⩒O₂peak = 58.8 ± 5.5 mL kg⁻¹ min⁻¹). Each trial started in the afternoon with an exhaustive cycling protocol. The following morning 1-h of steady-state cycling (SS) was followed by a time trial (TT). Carbohydrates (CHO) were not ingested in recovery from exhaustive exercise or during next day exercise in the Placebo trial (PLA); CHO were not ingested during recovery but were fed (15 g every ∼15-min) from 30-min into SS and continued during the TT in the delayed feeding trial (DELAY); CHO were provided during recovery (1.2 g/kg/h for 7 h) and next day exercise (as in DELAY) in a third condition (CHO). Exercise metabolism was assessed using indirect calorimetry and blood sampling. Fat oxidation rates during SS were similar in PLA (0.83 ± 0.17 g/min) and DELAY (0.78 ± 0.14 g/min) (p > 0.05) and higher than CHO (0.57 ± 0.27 g/min) (p < 0.05). There were no significant differences in TT performance (49.1 ± 10.7, 43.4 ± 7.6, 41.0 ± 7.9 min in PLA, DELAY and CHO, respectively; p > 0.05). Delayed carbohydrate feeding could be a strategy to maintain high-fat oxidation rates typically associated with exercise undertaken after the sleep-low approach to training but the acute performance effects remain inconclusive.