Gut training: intestinal adaptation to race nutrition

Progressively conditioning the digestive system to absorb large amounts of carbohydrates during exercise.

In Ironman competition, the target is 60-90 g of carbohydrates per hour, sometimes more. The problem: most athletes cannot tolerate these amounts without prior training. Gut training means progressively consuming more carbohydrates during long training sessions, starting at 30-40 g/h and increasing by 10-15 g/h per week. The gut adapts by upregulating SGLT1 and GLUT5 transporters to absorb more glucose and fructose simultaneously. Typical progression takes 4-8 weeks. Practically: train with the exact race-day products (same brand, same flavour) to test gastric tolerance at race-pace intensity.