“More marathons are won or lost in the porta-toilets than at the dinner table”. These words by Bill Rodgers, a four-time winner of the Boston Marathon, highlight the scale of gastrointestinal ailments that occur in athletes.

mgr Dominika Kuczyńska-Schulz

Among the group of people training, digestive tract ailments are very common occurring in 30-50% of athletes — some sources estimate it as high as 70% — with more frequent occurrence among women and runners. Intensive exertion coupled with dehydration is the cause of gastrointestinal symptoms such as nausea, vomiting, stomachache, bloating, and diarrhea. These symptoms are observed 1.5-3 times more frequently among athletes than among the recreational exercise population.

Splanchnic hypoperfusion

During intensive physical exertion, the intestinal epithelium becomes damaged primarily due to splanchnic hypoperfusion. Splanchnic blood flow decreases proportionally with increases in the intensity of the exercise. During maximum exertion it can be reduced by even 80% compared to the value at rest. The change in circulating blood distribution, with noticeable ischemia of the abdominal organs, significantly increases the risk of intestinal epithelium damage due to hypoxia. ATP depletion occurs at the cell level in the condition of hypoxia. Adenosine triphosphate is the compound which is the main source of cell energy and when reduced leads to the death of the cell and the development of an inflammatory condition which, combined with hyperthermia, may lead to leakage in the tight junctions of the intestinal epithelium. This causes an increase in the permeability and translocation of undigested food particles, bacteria, and pathogens from the intestinal lumen to circulation. It leads to endotoxemia, which induces an increase in the concentration of pro-inflammatory cytokines and a further increase in body temperature during physical exercise.

druzynaMechanical factors

The negative impact of physical exercise on the digestive system is also connected with mechanical factors impacting the abdominal organs, including increased pressure in the abdomen as well as vibrations and shocks while running. The specific position taken by cyclists (particularly in the aerodynamic posture) causes increased pressure on the abdomen resulting in more frequent exposure to symptoms in the upper digestive tract (esophagus and stomach).

Nutritional factors

Nutritional factors including the kind of food consumed may exacerbate the occurrence of digestive tract ailments even more. Research has proven that there is a very close dependency between the level of exacerbation of these ailments and diet. Their risk of occurrence was much higher after consuming food rich in dietary fiber, fats, proteins, and concentrated carbohydrate drinks. An additional factor worsening gastrointestinal ailments is dehydration resulting from insufficient consumption of liquids. Triggered by hypoperfusion, the increased permeability of the intestinal mucosa causes partially digested food to move to the submucosal muscular coat and to blood vessels, which induces a defensive inflammatory reaction of the immune system. The increase in the concentration of pro-inflammatory factors causes the exacerbation of gastrointestinal syndromes as well as systemic ones and symptoms in other tissues and systems. It may also result in higher susceptibility to infection or autoimmune disease. Disorders in digestive system functions may result in a decrease in the quantity of consumed food leading to a negative energy balance and, consequently, to impaired adaptation to increased training loads. Ailments of the digestive tract may significantly limit the intensity of physical effort and frequently be the cause of the inability to take part in training or a competition.

Dziewczyna biegnie

Carbohydrates during physical effort

Guidelines for athletes’ nutrition clearly define the importance and the quantity of carbohydrates which should be consumed by participants of various disciplines depending on the duration and the intensity of physical training. At the same time, it is thought that concentrated carbohydrate drinks (hypertonic with the concentration of carbohydrates > 8g/100ml) intensify gastrointestinal symptoms such as a delay in stomach emptying and a decrease in water absorption. The results of examinations of athletes in different disciplines have not definitively established the impact of carbohydrate supply during exercise on the occurrence of gastrointestinal ailments. As many sportspeople do not realize that there is an upper threshold to carbohydrate absorption, they frequently exceed the daily limit of consumption of 60g/hour (1g/min) putting themselves at risk of such ailments. The carbohydrate consumption limit is conditioned by the pace of oxidation, which amounts to around 1g/min. Combining simple sugars (glucose, fructose) with maltodextrins (polysaccharides obtained from crops) gives increased carbohydrate oxidation up to 1,2-1,75 g/min. However, it must be noted that maltodextrins may trigger allergic reactions, intestinal ailments and have a negative influence on microbiota. In instances of digestive tract ailments, key factors may be the amount taken, the kind of carbohydrates and their concentration in a drink or gel, as well as the other constituent substances (colorings, preservatives, antioxidants, thickeners, flavor enhancers, etc. so abundantly used by producers of nutrients and supplements for sportspeople).

“Training the gut” – nutritional training

Sports training is aimed at inducing adaptative changes in the cardiovascular, respiratory and muscular systems. Can one train the digestive system, which also needs to adjust to the conditions of hypoxia and hyperthermia as well as a large volume of consumed food and drinks? Yes, one can, although it must be remembered that immediate effects won’t be achieved. Development of strategies, reactions, regulations and mechanisms reducing the occurrence of ailments requires self-observation, gradual implementation of changes, and time. Research shows that for athletes who are not used to consuming drinks and food during exercise these ailments occur twice as often as in athletes regularly consuming them. With nutritional training one can increase the absorption of carbohydrates (an increase in oxidation), however it does not have a direct impact on the increase in the storing of glycogen and the expression of transporter proteins (e.g. GLUT 4 glucose transporter). One may conclude that proper “training the gut” allows for an adaptation to higher consumption of nutrients and lowering the risk of digestive tract ailments occurring. It is recommended, therefore, that athletes define individual tolerances for particular diet strategies in order to choose the best one.

Non-steroidal anti-inflammatory drugs (NSAIDs)

The use of non-steroidal anti-inflammatory drugs is very common among athletes, becoming more frequent as training experience grows. The risk of intestinal epithelium damage in people using NSAIDs is 3-5 times higher than in non-users. Ibuprofen increases the damage to the intestinal epithelium induced by physical exertion, which leads to the worsening of the intestinal barrier function. The use of non-steroidal anti-inflammatory drugs is detrimental and should be advised against in athletes reporting persistent and recurring ailments of the digestive tract.


In recent years more and more attention has been paid to the importance of probiotics in the intestinal barrier function. The beneficial effects of probiotic strains rely on decreased damage to the mucous membrane of the digestive tract and the lessening of inflammatory conditions. Probiotic bacteria — in particular from the Bifidobacterium and Lactobacillus families — lower the synthesis of endotoxins and decrease their absorption, which leads to lower inflammatory conditions. When synthesized by probiotic bacteria, short-chain fatty acids (SCFA) are a source of energy for intestinal epithelium cells, stimulating mucus production and antibacterial activity against pathogenic flora.

Research on athletes administered poly-probiotics showed them to have a reduced concentration of pro-inflammatory cytokines, markers indicating damage to the intestinal barrier, and significant reduction in gastrointestinal ailments and upper respiratory tract infections, thus demonstrating clearly that this group may benefit from the use of probiotic supplements.

Probiotic use may significantly reduce the incidence and exacerbation of digestive tract ailments and have a beneficial effect on intestinal epithelium integrity, reduce inflammatory conditions, and increase nutrient absorption and the bioavailability of mineral substances.

kobieta na rowerze

Nutritional modifications – practical guidelines

In order to reduce gastrointestinal ailments, the following guidelines might be helpful:

  • avoiding fiber-rich food both on the day of a competition and the day before
  • avoiding derivatives of salicylic acid and non-steroidal anti-inflammatory drugs and painkillers
  • avoiding high fructose food (especially drinks containing glucose-fructose syrup and sweetened with fructose: fruit juices, drinks, jams, sweets, syrup)
  • avoiding dehydration, which to a significant extent exacerbates gastro-intestinal ailments
  • starting training and competitions in a state of maximum hydration
  • consuming carbohydrates during physical exercise with a proper amount of water
  • avoiding concentrated carbohydrate drinks due to their osmolality (hypertonic drinks) both 30-60 minutes before physical exercise and during it.
  • testing new nutrient strategies, although it should be noted that reactions to the same food or nutritional plan can differ widely between people: what works for one person may not work for another.
  • considering performing the MRT test and following a diet in accordance with the LEAP Program.

Eliminating foods that exacerbate inflammatory conditions

Due to the impairment of the intestinal barrier function in athletes resulting mainly from the physiology of physical exertion (limiting splanchnic circulation), together with an increase in pro-inflammatory cytokines concentration, a beneficial strategy might be identifying and eliminating these foods and food additives (colorings, preservatives, artificial sweeteners that are ingredients of many sports supplements), which exacerbate inflammatory reactions.

The Mediator Release Test (MRT) may help in the development of such a nutritional map. It examines the reaction of leucocytes to 150 foods and chemical substances (preservatives, non-steroidal anti-inflammatory drugs, and substances naturally occurring in food, e.g. solanine, fructose).

Eliminating foods that exacerbate inflammatory conditions can serve to limit digestive tract ailments, improve immunity and reduce systemic inflammatory conditions, which directly impact increased capacity and quicker recovery after exercise.

Developed using the MRT tests results, a LEAP Program (Lifestyle, Eating and Performance) is a good solution when identifying the individual nutritional strategy which is the most beneficial for an athlete. Enabling the exclusion from the diet of products that trigger excessive inflammatory reactions limits the adverse influence of food on the digestive tract and leads to a diet consisting of the safest components. Additionally, the Leap Program is an ideal element of nutritional training because it forces a thorough review of products and analysis of their content (both foods and nutrients). Introducing a rotation in a diet prevents the accumulation of food antigenes in the blood stream and increases the pro-inflammatory response of the immune system. It can lead to a reduction of a persistent inflammatory condition, which is actually higher in athletes than in people pursuing moderate physical activity.

A diet based on MRT test results and the LEAP Program’s assumptions must be individually developed for each athlete by a Certified Consultant of the LEAP Program who has knowledge of sports physiology and the rules of sports nutrition.

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