Training the gut

Training the gut is a sports nutrition strategy designed to allow athletes to handle increased amounts of food and fluid to meet their training and competition requirements.

Gastrointestinal symptoms

Many athletes, particularly those participating in intense and/or prolonged exercise, suffer from gastrointestinal (GI) discomfort.

The symptoms are highly individual and can include bloating, abdominal cramping, diarrhea and vomiting (1, 2). On the most severe end of the spectrum, athletes may experience ischemic colitis and small bowel infarctions, which may require surgical resection (2). Regardless of severity, GI symptoms can certainly affect both performance and recovery (2).

Factors

The following factors play a role in the development of gastrointestinal symptoms in athletes:

High intensity and/or long duration exercise
Hot environment
Dehydration
Large amounts of fluid and/or carbohydrate intake required for performance (1)

Causes

As seen in the article Exercise, gut health and gastrointestinal issues, there are multiple physiological and mechanical causes leading to GI symptoms during exercise. The end result is a decreased absorption of fluid and nutrients (1, 2).

Despite many athletes expressing their frustration with their ability to “stomach” food and/or fluids during training and competition, the gastrointestinal tract can adapt to changes. This means that you can train your gut to be able to take more food and fluids without feeling discomfort.

Training the gut can result in positive changes such as increased carbohydrate oxidation and increased gastric emptying (i.e., the rate at which the stomach contents move to the intestine) (2, 3), leading to decreased discomfort and better absorption of nutrients (3). Notably, there is some evidence that symptoms can improve regardless of gut function improvements (2).

Breaking limits

The main fuel source during endurance exercise is carbohydrate. The requirements increase with intensity and duration of exercise and are expressed as grams per hour (g/h). On average, carbohydrate can be oxidised at a maximum rate of 60 g/h. When a higher intake is required, the addition of multiple transportable carbohydrates (e.g. glucose, sucrose, maltose, maltodextrin, starch) as opposed to a single one can increase this oxidation rate (1, 4). In practice, rates of over 90 g/h can be achieved using this strategy, especially in athletes who are used to consume large amounts of carbohydrate (4). The most utilised combination is fructose + glucose likely due to availability of commercial products.

Practical considerations

Training the gut is like training the muscles: it takes time, planning and patience. In addition, each athlete needs to figure out what works for them, ideally with the guidance of a qualified sports dietitian. The most important practical considerations are:

Know your needs. Not every athlete needs to train their gut. For example, if you participate in shorter endurance exercise, non-endurance activities or if you don’t rely on carbohydrate for fuel (e.g. fat-adapted endurance athletes), there is no need for you to train your gut.
Do not test approaches in competition. As mentioned before, training the gut takes time, so ideally you want to start as far away to competition as possible.
Make sure you test approaches in key training sessions, i.e. sessions that closely resemble the actual competition.
Take into account food intolerance. Some carbohydrate source can cause gastrointestinal issues due to intolerance (e.g. certain FODMAPs). Therefore, you want to use carbohydrate sources that are less likely to cause issues.
Get comfortable with being uncomfortable. Many athletes avoid eating close to and during exercise because they are not used to exercising on a full stomach. This discomfort will decrease with time but you need to battle through discomfort in the beginning.
Measure the outputs. Training the gut does not always lead to increased performance or decreased GI symptoms. If you are not achieving benefits from this approach, it is probably not worth pursuing.
Don’t copy what other athletes do. Work with a sports dietitian to figure out your requirements and the best strategy to optimise your performance and recovery.

References

Jeukendrup AE. Training the Gut for Athletes. Sports Med. 2017 Mar;47(Suppl 1):101–10.
de Oliveira EP, Burini RC, Jeukendrup A. Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sport Med. 2014/05/06. 2014;44 Suppl 1(Suppl 1):S79-85.
Jeukendrup AE. Periodized Nutrition for Athletes. Sports Med. 2017 Mar;47(Suppl 1):51–63.
Costa RJS, Young P, Gill SK, Snipe RMJ, Gaskell S, Russo I, et al. Assessment of Exercise-Associated Gastrointestinal Perturbations in Research and Practical Settings: Methodological Concerns and Recommendations for Best Practice. Int J Sport Nutr Exerc Metab [Internet]. 2022;32(5):387–418. Available from: https://journals.humankinetics.com/view/journals/ijsnem/32/5/article-p387.xml

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Training the gut