How to optimize your endurance sports performance with Gut Training: dietary strategies for efficient digestion

Training is fundamental. Nutrition is too. During long-distance events, whether trail running, triathlon, or cycling, the goal is to meet your needs without causing digestive issues. To achieve this, there is also a type of training known as Gut training, which means “training to eat” or “intestinal training”. In endurance sports, fueling is essential; however, it is not always easy. Sometimes intestinal issues appear and effort becomes more difficult (cramps, bloating, a feeling of heaviness, nausea, etc.). As endurance athletes involved in demanding disciplines such as trail running, triathlon, or ultra-cycling, you know better than anyone how crucial nutrition is for maximizing performance. But did you know that the secret to achieving your goals could lie in what is known as "Gut Training"? Gut Training is a method designed to reduce gastrointestinal discomfort in athletes who want to consume high amounts of exogenous carbohydrates during exercise. It optimizes intestinal function to improve your tolerance to carbohydrates during the most demanding events.

• Understanding digestive issues

Digestive issues are a complex challenge for endurance athletes, capable of turning hours of training into either a resounding success or a grueling ordeal. Factors such as previous meals, the state of the gut microbiota, and nutrition and hydration during the event all play a crucial role in this phenomenon.

A study of 63 marathon runners found that 54% experienced digestive issues, including 20% who reported post-training diarrhea. In addition, 13% of the runners had traces of blood in their stools.

Another study focusing on triathletes highlighted differences in the prevalence of digestive issues depending on the type of endurance activity practiced. For example, 49% of the participants surveyed reported digestive issues, mainly during running. In addition, it was observed that 93% of those who vomited had consumed hypertonic drinks, while 100% of those who vomited had eaten within the 3 hours preceding the race, and 100% of those who experienced stomach pain had consumed whole grains rich in fiber.

These studies highlight the significant impact of running on digestive issues. Although these problems can occur in all endurance activities, such as cross-country skiing, cycling, or race walking, they are much more common in running because of the repeated impact the body experiences with each stride.

Digestive issues during exercise are therefore two to three times more common in running, because shock waves affect the digestive tract, increasing in particular the prevalence of diarrhea and gastrointestinal bleeding. This incidence is even more pronounced during prolonged efforts such as trail races or ultra-trail races. One possible strategy to address this is to refuel during climbs and avoid doing so at the summits, where impacts are greater and vibrations transmitted to the internal organs are intensified.

Digestive issues during exercise are multifactorial. They may be caused by stress or anxiety about the event, position (particularly on the bike), bouncing movements (while running), a history of digestive issues (if you have experienced them in the past), blood flow during exercise (blood is directed toward the muscles during exertion rather than the intestines), exercise intensity, hormones, heat, and nutrition.

Indeed, people often believe that digestive issues are caused solely by nutrition, but all the other factors mentioned above can also play a role. Nutrition can cause digestive issues, particularly through the consumption of fiber, the consumption of fat, dehydration, poor absorption of carbohydrates, eating a large meal before exercise, very sweet flavors, and lactose. It is possible to act quickly by reducing fiber and fat intake before exercise, as well as avoiding large meals and lactose. Poor carbohydrate absorption, however, must be trained to improve tolerance.

• What are the benefits of intestinal training?

Endurance sports are highly demanding on the body when you experience physical suffering, but also on all the organs, especially the intestines, which endure numerous stresses during exercise. The benefits of training the intestines include:

-Reducing or eliminating digestive issues during exercise
-Improving the transport and use of nutrients

If you experience stomach or intestinal discomfort during exercise, Gut training is an effective way to:

-Reduce intestinal discomfort
-Improve gastric emptying
-Reduce bloating
-Tolerate larger volumes
-Improve the rate at which carbohydrates can be absorbed

• How can you establish effective intestinal training?

Two approaches are possible:

1. Intestinal training: Just as with physical training, it is possible to strengthen the intestines. The stomach is an adaptable organ, which means that with appropriate training, it can better tolerate carbohydrate intake. This practice, often called "stomach training," has two main benefits: the stomach can expand to accommodate a larger amount of food, and a full stomach is better tolerated and less uncomfortable, thereby improving comfort during exercise.
2. Carbohydrate consumption: Improved gastric emptying varies according to the nutrient (better tolerance to glucose when glucose is used and better tolerance to fructose when fructose is used). Better absorption of glucose in the intestines can reduce negative feedback, which could promote more efficient gastric emptying and better use of carbohydrates during exercise.

• And in practice, how should you do it?

Intestinal issues during races are not inevitable and can be greatly reduced, or even avoided, with a few simple tips.

• Avoid new foods before the competition and stick to foods you know.
• Reduce fiber intake a few days before the event to avoid intestinal irritation. If you are sensitive to these problems, reduce your intake a few days before the event.
• Test nutrition and hydration products regularly under the same conditions as during the race to assess their effects on you. Studies have shown that athletes who are not accustomed to consuming liquids and food during exercise are more likely to develop gastrointestinal symptoms.
• Become familiar with the flavors and textures, and note the effects of refueling so that you have no surprises on race day.
• Follow your nutrition plan to maintain regular eating habits and avoid the risks associated with intuitive eating.
• Include high-carbohydrate days in your training if you follow a low-carbohydrate or high-fat diet in order to improve stomach tolerance and comfort.
• Try a short-term reduction in FODMAPs if you suffer from gastrointestinal issues.
• Practice drinking during training sessions. Hydrate sufficiently before and during exercise to prevent dehydration.
• Limit medication use and consult a gastroenterologist in the event of persistent gastrointestinal issues.

Before a race:

• Maintain a high-energy, high-carbohydrate diet before the competition to maximize glycogen stores.
• Limit insoluble fiber intake and eat your pre-competition meal at least 3 hours before the warm-up. Favor fast-digesting proteins and limit fats. Avoid overeating before and during exercise.
• Current recommendations advise a carbohydrate intake of up to approximately 60 g for exercise lasting up to 2 h. When exercise lasts more than 2 h, slightly higher amounts of carbohydrates (90 g / h) are recommended. These carbohydrates should consist of a mixture of several carbohydrates (glucose:fructose (2:1) or maltodextrin: fructose (2:1)).
• In hot conditions, it is useful to begin hydrating before exercise to stimulate gastric emptying.
• Practice the race nutrition and hydration plan several times.
• Start the race well hydrated. Use clear urine as your guide.

These tips are essential for establishing effective intestinal training and promoting optimal performance during your sporting activities.

In conclusion, optimizing performance requires appropriate nutrition and efficient digestion. Gut Training, or intestinal training, is a promising strategy to reduce digestive issues and maximize nutrient absorption during exercise. By understanding the many factors that affect intestinal health, you can implement specific nutrition and hydration practices to prevent gastrointestinal discomfort. By combining physical training with stomach training and an appropriate nutrition strategy, you can improve comfort during exercise and optimize your performance over the long term.

Halvorsen, F. A., Lyng, J., & Ritland, S. (1986). Gastrointestinal bleeding in marathon runners. Scandinavian Journal of Gastroenterology, 21(4), 493–497.

Rehrer, N. J., van Kemenade, M., Meester, W., Brouns, F., & Saris, W. H. M. (1992). Gastrointestinal complaints in relation to dietary intake in triathletes. International Journal of Sport Nutrition and Exercise Metabolism, 2(1), 48–59.

This article was written in partnership with Marine Lecuisiner