Training the gut

Asker Jeukendrup’s point of view

As discussed before, carbohydrate intake during training can help performance. However, taking too much can also cause stomach and gut problems.

Stomach and intestinal problems are very common in endurance sport, especially in running. Often athletes take gels and carbohydrate drinks and this can lead to a bloated feeling and several other gastro-intestinal problems.

Although most gastro-intestinal problems do not seem to be related to intake during the race but rather with factors not related to nutrition or factors related to the intake the days leading up to a race, it is clear that we need to balance the intake of gels, drinks and bars during activity to make sure we provide enough energy but do not cause gastro-intestinal problems.

The gut: an extremely adaptable organ

However, there is one other approach that may work. The gut is an extremely adaptable organ and can be “trained” in a similar way to the way we train the muscle.


In a recent review in Sports Medicine, I have discussed the evidence that the gut can be trained. A lot of this evidence comes from studies in animals. But the evidence is strong and we also have a few human studies that point in the same direction. Contestants in eating competitions are known to ‘‘train’’ their stomach to hold larger volumes of food with less discomfort and – through regular training – are able to eat volumes of food within a small time-window that are unthinkable for the average and untrained person.


The current all-time record is 69 hot dogs (with bun) in 10 min. To achieve this, competitive eaters train using a variety of methods: chewing large pieces of chewing gum for longer periods of time or stomach extension by drinking fluids or by eating the competition foods. Volumes are progressively increased, and it takes many weeks to reach a level where these eaters can be competitive.



The stomach training

This demonstrates the adaptability of the stomach. Conducting this “stomach training” has two main effects:


1. the stomach can extend and contain more food;


2. a full stomach is better tolerated and is not perceived as so full.


Both aspects could be relevant to an exercise situation.

The intestinal absorption

Another example relates to intestinal absorption: carbohydrate absorption during exercise seems limited to about 60 g per hour (at least when a single type of carbohydrate, for example glucose, is ingested). An intake much above 60 g per hour will most likely result in accumulation of carbohydrate in the intestine. However, increasing daily carbohydrate intake, mostly by increasing intake during the activity, has been shown to increase the absorption and oxidation of ingested carbohydrate.

From theory to practice

How long it takes for this adaptation to take place is unknown, but in animal studies significant changes can be observed after a change of diet for only 3 days. The human study referred to above used 28 days. From a practical point of view, I have been recommending 5-10 weeks, at least once a week. (Please note that in the absence of concrete evidence this is a best guess based on information that is available). It may be best to pick one longer training session per week, or the training that is closest to the race the athlete is preparing for and use this to practice the race nutrition intake.


The opposite is also true, if an athlete never uses gels and drinks in training and then competes with large amounts of gels, drinks bars etc, this is a recipe for disaster. The gut is “untrained” for what it is asked to do and will not be able to cope… in this case, the athlete should blame him or herself and not the gels! So, make sure that “gut training” is part of your preparation for longer races.



  • Jeukendrup AE. Training the gut for athletes. Sports Med. 2017 Mar;47(Suppl 1):101-110.
  • Cox GR, Clark SA, Amanda J, Cox AJ, Halson SL, Hargreaves M, Hawley JA, Jeacocke N, Snow RJ, Yeo WK, Burke LM. Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. J Appl Physiol (1985). 2010 Jul; 109(1):126-134

Professor Asker Jeukendrup is one of the world’s leading sports nutritionists/ exercise physiologists who spent most of his career as a professor at the University of Birmingham (UK). Dr Jeukendrup authored 8 books and over 200 research papers and book chapters. His expertise stretches from exercise metabolism and sports nutrition to training and overtraining. He is currently a (visiting) professor at Loughborough University and director of his own performance consulting business “Mysportscience” and communicates science through the popular website Asker works as Performance Manager for the Dutch Olympic team and is Head performance Nutrition for the Lotto Jumbo Pro cycling team. He also works with FC Barcelona, and other elite football clubs. Asker practices what he preaches and completed 21 Ironman races including 6 time the Ironman world Championship in Hawaii.