Carbohydrate feeding and exercise recovery: effects on metabolism and performance

The importance of sufficient amounts of carbohydrates for optimal performance during endurance exercise is well established. However, it has been demonstrated that a high carbohydrate availability before, during and after training sessions could suppress molecular signalling pathways thought to be important for subsequent training adaptations and/or hinder training adaptations. In addition to that, evidence is inconclusive when it comes to the role of different monosaccharides during the short-term recovery after exhaustive exercise, i.e., how different monosaccharides affect recovery and metabolism during the subsequent exercise bout. The aim of this thesis was to uncover some of the pertaining questions in these areas. The aim of the first study was to explore a novel approach to sleeping and training with reduced carbohydrate availability whereby carbohydrates are ingested with a delay during a subsequent morning exercise bout. It was found that delayed carbohydrate feeding during exercise following a sleep low approach to training did not supress high fat oxidation rates typically observed under conditions of low carbohydrate availability. However, performance outcomes of the study did not show any significant differences, but there was a trend towards rescuing some of the performance that was lost as a result of avoiding carbohydrates during the recovery. The aim of the second study was to compare glucose only or fructose-glucose co-ingestion during the post-exercise recovery period on metabolism and performance during a subsequent exercise bout. Study results showed no performance benefits of fructose-glucose co-ingestion as compared to glucose only. However, the fructose-glucose combination led to higher oxidation rates of during recovery ingested carbohydrates during the subsequent exercise bout, hinting at increased whole-body post-exercise glycogen storage. The final study’s aim was to investigate the efficacy of galactose ingestion alone or in combination with glucose during the recovery after glycogen reducing exercise on muscle glycogen synthesis, and metabolism during a subsequent exercise bout. Glucose was shown to be a superior source for post-exercise muscle glycogen repletion over galactose or a combination of galactose and glucose. Interestingly, galactose ingestion resulted in substantial replenishment of muscle glycogen stores similar to those observed with a moderate glucose intake (galactose-glucose combination) without a rise in glucose and insulin levels suggesting that there might be a mechanism for a direct conversion of galactose into glycogen in the muscle. Collectively, the findings of the work contained within this thesis have successfully advanced the current knowledge in the area of sports nutrition and opened up new interesting questions that require further investigation