Gut training: più energia senza problemi digestivi

Q: Why do digestive problems arise in endurance sport?

The main limitation is not digestion in the muscles, but the ability of the intestines to absorb carbohydrates. The SGLT1 transporter can process only about 60 g of glucose an hour. Surplus carbohydrates stay in the intestine, draw in water and cause bloating, cramps or diarrhoea.

Q: What is gut training?

Gut training is targeted training of the digestive tract which improves the ability of the stomach and intestines to cope with higher volumes of fluid and carbohydrates during exercise. It works on the principle of adaptation, in the same way as training muscles.

Q: How far in advance should you start gut training?

Experts recommend starting 6 to 10 weeks before the race with a frequency of at least once a week, ideally during a longer session whose profile matches the upcoming race.

Q: What should you avoid before a race because of digestive problems?

Limit fibre, lactose and foods high in FODMAPs. Avoid drinks in which fructose is the only carbohydrate, and non-steroidal anti-inflammatory drugs such as ibuprofen. Do not forget to start drinking in good time.

21 giugno 2026Michal Jetelina0 commenti

Etichette

Nutrizione sportiva e fisiologia

Endurance sports such as marathons, triathlons or long-distance cycling require a constant supply of energy. The ideal scenario is topping up a sufficient amount of carbohydrates – but this often runs into the digestive problems faced by 30 to 50 % of endurance athletes. This creates the classic dilemma: take in fewer carbohydrates and risk running out of energy, or take in more and risk stomach trouble. The solution is “gut training" – targeted training of the digestive tract.

Gut training – training the digestive tract for endurance athletes

Why do digestive problems actually arise?

The main limiting factor for energy intake during exercise does not lie in the muscles, but in the ability of the intestines to absorb carbohydrates. If during exercise you take in only one type of carbohydrate (e.g. glucose), the body can process it at a rate of roughly only 60 g an hour – the limiting factor is the saturation of the SGLT1 transporter in the intestines.

How the intestine absorbs carbohydrates

Intestinal lumen
glucose, galactose, Na⁺

SGLT1

→

Enterocyte
cell of the intestinal wall

GLUT2

→

Blood
glucose

Intestinal lumen
fructose

GLUT5

→

Enterocyte
cell of the intestinal wall

GLUT2

→

Blood
fructose

Glucose and fructose use different transporters (SGLT1 vs. GLUT5) – which is why combining more types of carbohydrate makes it possible to absorb more energy per hour than a single carbohydrate on its own.

Adapted from Jeukendrup, 2017

If you take in more carbohydrates than the transporters can handle, they stay sitting in the intestine. There they draw in water, which leads to osmotic shifts, a feeling of fullness and subsequent problems such as diarrhoea or bloating.

Digestive problems, however, are not caused only by unsuitable sports nutrition – a combination of several factors is involved:

Redirection of blood – during intense exercise the body redirects blood to the muscles and skin, blood flow to the digestive tract can fall by up to 80 %, which causes ischaemia and cramps. Women are physiologically more prone to this.

The mechanics of the movement – runners suffer from the jolting of the stomach and intestines (damage to the lining, micro-bleeding), while cyclists in an aerodynamic position face pressure on the abdomen and reflux.

Pre-race stress – stress hormones change gut motility, shorten the time available for absorbing nutrients and often result in diarrhoea.

High osmolarity of drinks – strongly concentrated carbohydrate drinks (above 500 mOsm/L) draw water from the surrounding tissues into the intestines and can immediately trigger a feeling of a full stomach.

What is “gut training"?

The digestive tract is not a static tube, but a highly adaptable organ. Just as muscles respond to load with growth and better blood flow, the stomach and intestines can also adapt to what we ask of them. This adaptation can be illustrated by competitive speed eaters, who can train their stomach to hold enormous volumes of food without much trouble.

By loading the digestive system regularly you can train it in two respects:

Adaptation of the stomach

The stomach can stretch and hold more food or fluid, and after a few days it empties faster into the intestines. In athletes who repeatedly consumed large amounts of fluid while running, discomfort decreased significantly over time.

Adaptation of absorption

A repeatedly high-carbohydrate diet stimulates an increase in the number and activity of SGLT1 transporters. 28 days of training with a carbohydrate-rich diet dramatically increases the absorption and use of carbohydrates (Cox et al., 2010).

Gut training in practice

Experts recommend starting to train the digestive tract roughly 6 to 10 weeks before the race, with a frequency of at least once a week. It is enough to choose one longer session in the week, or a session whose profile most closely matches the upcoming race.

Gut training methods and their effects

METHODS

Large volume of fluid

Training straight after a meal

High carbohydrate intake during exercise

Simulating the race plan

More carbohydrates in the everyday diet

PHYSIOLOGICAL EFFECT

Less bloating and fullness
from:

Faster emptying of the stomach
from:

Higher capacity to absorb carbohydrates
from:

BENEFIT

Fewer digestive problems

Higher carbohydrate intake

→ Improved performance

Adapted from Jeukendrup, 2017

Sports science distinguishes several specific methods according to what exactly you need to improve:

Training stomach comfort (against the feeling of fullness) – during training, deliberately take in relatively large volumes of fluid. The stomach gradually stretches and the perception of discomfort and bloating decreases.

Training stomach emptying – go and train soon after a meal or after drinking a large amount of fluid. The body learns to move the contents of the stomach into the intestines faster even during exercise.

Training intestinal absorption – during selected sessions, deliberately consume high doses of carbohydrates. You force the intestines to increase the number and activity of transporters such as SGLT1.

Increasing carbohydrates in the everyday diet – moving from a diet of 40 % carbohydrates to 70 % can double the number of glucose transporters in the intestines within two weeks.

A full simulation of the race plan – in the weeks before the race, drink and eat exactly what you plan to consume on the day (gels, isotonic drinks, bars), at the same pace and with the same intervals.

Tip: what to avoid before a race

To minimise digestive problems on race day, what matters is not only what you eat, but also what you cut out of your diet in good time:

High fibre content (wholemeal bread, oats, raw vegetables) – keep your intestines relatively empty.
Lactose (ordinary milk) – even mild intolerance can cause problems during exercise; choose lactose-free, rice or soya milk.
Drinks with fructose as the only carbohydrate – it is absorbed more slowly and often leads to cramps or diarrhoea.
High FODMAP content – fermentable oligosaccharides, disaccharides, monosaccharides and polyols (wheat, dates, cherries) – they ferment quickly in the large intestine and increase osmotic pressure.
Aspirin and non-steroidal anti-inflammatory drugs (ibuprofen) – they increase the permeability of the intestinal wall.
Dehydration – it makes digestion worse, so do not underestimate drinking in good time.

Conclusion for athletes

Digestive problems in endurance sport are usually not a matter of bad luck, but a reflection of what our digestive tract can currently cope with. The digestive organs need to be trained with the same care as the muscles and the cardiovascular system. Thanks to gradual, systematic adaptation you will be able to absorb far more carbohydrates during exercise, improve your performance and enjoy the race much more.

References

Cox GR, Clark SA, Cox AJ, et al. (2010). Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. J Appl Physiol, 109:126–134.
Jeukendrup AE. (2017). Training the Gut for Athletes. Sports Med, 47(Suppl 1):101–110.
Jeukendrup A, Gleeson M. (2025). Sport nutrition (4th ed.). Human Kinetics.