Carbohydrate ingestion during exercise: effects on performance, training adaptations and trainability of the gut

Carbohydrate feeding has been shown to enhance endurance performance. During exercise of 2 h or more, the delivery of carbohydrates to the muscle is the crucial step and appears to be limited by intestinal absorption. It is therefore important to identify ways to overcome this limitation and study the positive and negative effects of chronic carbohydrate supplementation. There is evidence that intestinal absorption can, at least partly, be overcome by making use of multiple transportable carbohydrates. Ingestion of these carbohydrates may result in higher intestinal absorption rates and has been shown to lead to higher rates of exogenous carbohydrate oxidation which can result in better endurance performance. It also seems possible to increase the absorptive capacity of the intestine by adapting to a high-carbohydrate diet. Carbohydrate supplementation during exercise has been suggested to reduce training adaptations, but at present there is little or no evidence to support this. Despite the fact that it has long been known that carbohydrate supplementation can enhance endurance performance, there are still many unanswered questions. However, there is potential to develop strategies that enhance the delivery of carbohydrates and thereby improve endurance performance.