GI training

GI training refers to the deliberate practice of conditioning the stomach and intestines to handle larger volumes of fluid and carbohydrates during exercise. Endurance athletes use it to reduce gastrointestinal discomfort and optimise fuel and fluid absorption in events where nutrition plays a critical role.

Adaptation of the Digestive System

During prolonged exercise, blood flow is redirected away from the gut, slowing digestion and making it harder to tolerate food and drink. Research shows that the gut is trainable: repeatedly consuming carbohydrates and fluids during training sessions can increase gastric emptying rates, enhance the activity of glucose transporters (such as SGLT1) in the small intestine and reduce symptoms like bloating, cramping and diarrhoea. Gradually increasing carbohydrate intake from 30 g per hour up to 60‑90 g per hour using mixed glucose and fructose sources helps the intestine adapt to higher carbohydrate loads. Practising drinking larger volumes of fluid also expands stomach capacity, which can improve comfort during races. Athletes should implement GI training weeks or months before an event, starting with small amounts of the same drinks and foods they plan to use on race day. Consistency is key; occasional gut training sessions are less effective than regular practice.

Gut Conditioning Practices

Effective GI training strategies include simulating race nutrition during long runs or rides, sipping a carbohydrate-rich drink every 10‑15 minutes, and adding solid foods like bananas or rice cakes to accustom the stomach to mixed textures. Runners might schedule a weekly long run where they aim to consume 50 g of carbohydrate per hour, gradually increasing to 90 g. Cyclists often practise with two bottles: one with a sports drink and one with plain water, adjusting the ratio as tolerance improves. Using a combination of glucose and fructose allows the gut to utilise multiple transporters, increasing absorption without overwhelming a single pathway. Recording symptoms and adjusting volume, concentration and timing helps refine the plan. GI training should always be paired with adequate hydration and pacing; overloading the gut can still lead to distress.

Practising nutrition strategies trains the digestive system just as intervals train the muscles. By slowly increasing carbohydrate and fluid intake during training and using the same products planned for competition, athletes can minimise stomach issues, maintain energy availability and perform at their best.

Related Terms: Scheduled drinking, Carb‑only bottle, Non‑nutritive sweetener tolerance, Isotonic, Hypotonic