The gastrointestinal tract is highly adaptable and can be trained to absorb and tolerate larger amounts of carbohydrate during exercise, reducing the risk of race-day gastrointestinal distress. Repeated exposure to carbohydrate intake during training may increase gastric emptying efficiency and upregulate intestinal carbohydrate transporters (such as SGLT1 and GLUT5), enabling athletes to absorb well over 60 g/h and potentially exceed 120 g/h when using multiple transportable carbohydrates. For athletes new to high-carbohydrate fueling, it is recommend starting with 40–60 g of carbohydrate per hour and progressively increasing intake as tolerance improves while practicing the exact fueling strategy planned for competition. Ultimately, consistent gut training allows athletes to consume more carbohydrate with less discomfort, improving glycogen availability and supporting better endurance performance on race day.
Read more of Aaron's own words from the Carbs Fuel Website: https://carbsfuel.com/blogs/news/gut-training-for-fueling-and-performance