How to Train Your Gut for Endurance Sport: Why Daily Nutrition Matters
When endurance athletes think about gut training, they usually focus on practising their race fuelling strategy during long training sessions. While this is important, it’s only part of the picture.
Gut training doesn’t just happen during training — it also happens through your everyday nutrition.
Your digestive system adapts to what it is regularly exposed to. Just as muscles adapt to training load, the gut can adapt to the nutrients and quantities it processes. For endurance athletes, this is particularly relevant for carbohydrate intake, which is often consumed in large amounts during races and long training sessions.
Gastrointestinal Issues in Endurance Athletes
Gastrointestinal (GI) symptoms are common in endurance sport. Many athletes experience issues such as:
bloating
stomach cramps
nausea
reflux
diarrhoea
gels or sports drinks “sitting” in the stomach
These symptoms often occur when athletes try to consume more carbohydrate during exercise than their gut is accustomed to handling.
Research suggests that repeated carbohydrate exposure can support adaptations in the digestive system, including increased intestinal carbohydrate transport capacity and improved carbohydrate absorption during exercise. These adaptations can help athletes tolerate higher carbohydrate intake with fewer gastrointestinal symptoms (Jeukendrup, 2017).
Why Daily Nutrition Helps Train the Gut
While practising race fuelling during training is essential, daily nutrition also contributes to gut training.
Regular carbohydrate intake across the day exposes the digestive system to carbohydrate more consistently. Over time, this may support the gut’s ability to process and absorb carbohydrate efficiently when exercise intensity increases.
Diet composition also affects the gut microbiome, the community of microorganisms that live in the gastrointestinal tract. A varied diet containing sufficient carbohydrate and fibre supports microbial diversity, which may play a role in digestive health and tolerance during exercise (Clark and Mach, 2016).
For athletes aiming to increase carbohydrate intake during competition, both in-session fuelling practice and consistent daily nutrition are important.
Key Takeaway: Gut Training Happens Every Day
Athletes struggling with gastrointestinal issues during running, cycling or endurance racing often focus on changing gels or sports drinks.
However, improving gut tolerance may require a broader approach that considers both race fuelling strategies and everyday dietary habits.
Practising fuelling during training sessions is important, but what you eat every day also helps determine how well your gut handles fuel when it matters most.
How to Train Your Gut for Endurance Sport
Athletes can improve fuel tolerance by gradually exposing the gut to higher carbohydrate intake over time. Practical strategies include:
Practising race fuelling strategies during long training sessions
Gradually increasing carbohydrate intake during exercise
Consuming adequate carbohydrate across the day
Avoiding large increases in fuelling only on race day
Maintaining a varied diet including dietary prebiotics and probiotics, to support gut microbiome health
These strategies allow the digestive system to adapt to higher carbohydrate intake during exercise.
Frequently asked questions
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Gut training refers to gradually adapting the digestive system to tolerate carbohydrate intake during exercise by regularly practising fuelling strategies in training.
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Gastrointestinal symptoms often occur when athletes consume more carbohydrate or fluid during exercise than their gut is adapted to processing.
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Yes. Regular carbohydrate intake and overall diet composition can influence digestive adaptations and the gut microbiome, both of which affect fuel tolerance during exercise.
Need Help Improving Fuel Tolerance?
If you regularly experience stomach issues during training or races, reviewing both your daily nutrition and fuelling strategy may help improve tolerance and performance.
If you would like personalised support with your endurance sport nutrition strategy, you can learn more or get in touch through RJ Performance Nutrition.
Learn more about Rachel, sports dietitian and founder ot RJ Performance Nutrition here
References
Clark, A. & Mach, N. (2016). Exercise-induced stress behavior, gut-microbiota-brain axis and diet: a systematic review for athletes. Journal of the International Society of Sports Nutrition, 13(43).
Jeukendrup, A. (2017). Training the gut for athletes. Sports Medicine, 47(S1), 101–110.
Thomas, D.T., Erdman, K.A. & Burke, L.M. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine: Nutrition and athletic performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528.