Carbohydrate intake during endurance exercise is already a well established strategy to sustain performance, preserve glycogen stores and reduce the perception of fatigue. However, many athletes still experience gastrointestinal discomfort when trying to increase carbohydrate intake during training sessions and competitions.
What many athletes do not realize is that the gut can also be trained. Just like muscles and the cardiovascular system adapt to training stimuli, the gastrointestinal tract can develop greater tolerance and absorption capacity when progressively exposed to carbohydrate intake during exercise.
What is gut training?
Gut training is a strategy used to adapt the digestive system to frequent carbohydrate intake during training sessions and competitions. The goal is to improve gastrointestinal tolerance and increase nutrient absorption capacity, especially during prolonged exercise.
During long events such as marathons, triathlons and endurance cycling races, carbohydrate intake may exceed 60 g per hour and, in some cases, reach 90 g or more per hour. For many athletes, consuming these amounts without prior adaptation may lead to symptoms such as:
- nausea
- bloating
- reflux
- abdominal pain
- diarrhea
- loss of appetite
These symptoms not only affect comfort, but may also directly impair performance.
Why does the gut need to be trained?
During intense exercise, blood flow is redirected toward the working muscles and reduced in the gastrointestinal system. This temporarily decreases digestive capacity and may impair carbohydrate and fluid absorption.
In addition, when athletes suddenly increase carbohydrate intake without adaptation, the high concentration of nutrients in the intestine may delay gastric emptying and increase the risk of gastrointestinal discomfort.
With frequent practice, the body develops important adaptations, including:
- improved gastric emptying
- increased intestinal absorption capacity
- greater tolerance to different carbohydrate sources
- reduced gastrointestinal symptoms
- improved confidence with race day nutrition
These adaptations allow athletes to sustain more aggressive nutritional strategies, especially during long duration events.
How does carbohydrate adaptation happen?
Adaptation occurs mainly through increased activity of intestinal transporters responsible for carbohydrate absorption.
Glucose is primarily absorbed through the SGLT1 transporter, while fructose uses the GLUT5 transporter. When athletes regularly consume carbohydrates during training, the body increases the expression of these transporters, promoting greater absorption and lower gastrointestinal discomfort.
This is one of the reasons why strategies combining multiple carbohydrate sources, such as maltodextrin and fructose, are commonly used in endurance sports.
How to train the gut in practice
Gut training should be gradual and planned, always during training sessions.
Some practical strategies include:
1. Consume carbohydrates during long training sessions
Avoiding every session in a fasted state or without fueling helps the body adapt to carbohydrate intake during exercise.
Ideally, training nutrition should resemble the strategy planned for competition.
2. Increase intake progressively
Athletes with low carbohydrate intake can start with around 30 g per hour and gradually increase intake over the following weeks.
This progression allows the gastrointestinal tract to adapt with a lower risk of discomfort.
3. Test different formats and combinations
Gels, sports drinks, powdered carbohydrates and other formats may produce different responses in each athlete.
In addition, the combination of carbohydrate sources also influences gastrointestinal tolerance.
4. Simulate race day nutrition
Specific training sessions are the best opportunity to test timing, quantities, flavors and product concentrations.
This reduces unexpected issues and improves nutritional confidence for competition day.
How much carbohydrate should be consumed per hour?
Recommendations vary according to exercise duration and intensity.
In general:
- exercise lasting up to 1 hour may not require carbohydrate intake
- exercise between 1 and 2 hours may benefit from around 30 g to 60 g per hour
- exercise longer than 2 hours and 30 minutes may benefit from 60 g to 90 g per hour
In highly trained and adapted athletes, some current strategies are already investigating intakes above 90 g per hour. However, this approach requires proper gut adaptation.
Individuality matters
Not all athletes respond the same way to carbohydrate intake. Factors such as exercise intensity, pre race anxiety, hydration status, environmental temperature and gastrointestinal history directly influence food tolerance.
For this reason, nutritional strategies should be individualized and adjusted according to the athlete’s experience, sport and race goals.
Practical application in endurance sports
In endurance sports, the ability to consume and absorb carbohydrates during exercise can be just as important as physical training itself.
Athletes who neglect gut training may achieve good training loads, but struggle to sustain their nutrition strategy during competition.
Training the gut means preparing the body to efficiently utilize carbohydrates, reducing discomfort and supporting a more consistent energy delivery throughout the event.
Conclusion
The gut is also part of sports performance. Just like muscles, the heart and the respiratory system adapt to training, the gastrointestinal tract also responds to the frequent stimulus of carbohydrate intake during exercise.
Gut adaptation may improve food tolerance, increase carbohydrate absorption and reduce gastrointestinal discomfort during endurance events.
For this reason, nutrition strategies should never be tested only on race day. Gut training needs to be part of the athlete’s routine.
