Irritable bowel syndrome in athletes: causes and the link with load and pharmacology

A sudden need for the toilet in the middle of a run, bloating after a protein shake, alternating diarrhea and constipation during the competitive period - for many athletes this is an everyday reality. Some of these complaints fit the picture of irritable bowel syndrome (IBS). The editors explain what IBS is from the standpoint of modern medicine, how training interacts with it and which components of sports nutrition and medications can worsen the symptoms.

What irritable bowel syndrome is

Irritable bowel syndrome is a functional disorder, or, in modern terminology, a disorder of the 'brain-gut' interaction. It manifests as recurrent abdominal pain associated with defecation or a change in the frequency or consistency of stools, in the absence of structural changes that would explain the symptoms.

The diagnosis is made according to the Rome IV criteria (2016): abdominal pain at least once a week over the last three months, associated with defecation, a change in the frequency or form of the stool, provided that the symptoms began at least six months ago. Depending on the predominant stool type, IBS with constipation, with diarrhea, mixed and unclassified variants are distinguished.

IBS is one of the most common gastroenterological conditions in the world; women suffer from it more often than men. Athletes are not protected from it, and the specific conditions of sport - stress, a particular diet, intense loads - can aggravate the symptoms.

It is important to distinguish IBS from the so-called exercise-induced gastrointestinal syndrome, which occurs in many endurance athletes only during or after prolonged work. These conditions overlap, but the first is a chronic disorder, and the second is mainly a situational reaction to training.

The 'brain-gut' axis and why stress matters

The gut has its own nervous system, which is closely connected to the central one through the vagus nerve, the spinal cord, hormones and immune signals. In IBS this connection is disrupted: visceral hypersensitivity arises, when ordinary stretching of the intestine is perceived as pain, and motility changes.

Stress is one of the most powerful modulators of this axis. Pre-start anxiety is familiar to almost every athlete: more frequent urges, a 'rumbling' stomach, accelerated transit. In people with IBS this reaction is much stronger and can last for days before an important competition.

Other mechanisms discussed in the literature are changes in the gut microbiota, minimal inflammation of the mucosa, increased permeability of the intestinal barrier and disturbances in serotonin metabolism. Post-infectious IBS is singled out separately; it develops after an acute intestinal infection - for example, 'traveler's diarrhea' during camps or competitions abroad.

Such an understanding explains why in IBS not only diet and drugs are effective, but also psychological methods - cognitive behavioral therapy and gut-directed hypnotherapy. This is recognized by the guidelines of the British Society of Gastroenterology (2021) as well.

Load: benefit and harm for the gut

Regular moderate physical activity is generally beneficial for people with IBS. In the randomized study by Johannesson et al. (2011) an increase in physical activity reduced the severity of symptoms compared with the control group. Guidelines include physical activity among the basic recommendations.

However, in elite sport the situation is more complicated. During intense and prolonged work, blood flow in the gut decreases, the mucosa undergoes ischemia, its permeability increases and motility changes. The mechanical jolts of running additionally stimulate the large intestine. In people with an already sensitive gut these changes provoke a flare-up.

• running provokes intestinal symptoms more often than cycling or swimming;
• heat and dehydration intensify mucosal ischemia;
• an intensity above the athlete's threshold increases the risk of symptoms;
• pre-start stress adds to the physiological changes;
• training immediately after eating worsens tolerance.

Interestingly, the gut, like the muscles, is partly 'trainable'. Systematically consuming carbohydrates during training improves their absorption and reduces symptoms in competition. This approach is actively discussed in the sports nutrition literature.

So the question is not whether people with IBS should train, but how to structure the load, nutrition and recovery so that the symptoms do not limit performance and quality of life.

Sports nutrition and supplements as triggers

An athlete's diet often contains foods that people with IBS tolerate poorly. The key concept here is FODMAP: a group of short-chain carbohydrates that are poorly absorbed in the small intestine, attract water and are fermented by bacteria, causing gas formation. A low-FODMAP diet has an evidence base in IBS.

Protein bars and 'low-calorie' desserts are a typical source of sugar alcohols, which can be consumed by athletes in significant amounts during 'cutting'. Sorbitol and maltitol have a pronounced osmotic effect; erythritol is usually better tolerated, but individual sensitivity varies.

Whey protein concentrate contains lactose, whereas isolate and hydrolysate contain much less. People with lactase deficiency and IBS are often helped by switching to isolate or another protein source. Carbohydrate drinks with a high proportion of fructose may be poorly tolerated; a combination of glucose and fructose in a certain ratio is usually better tolerated than pure fructose.

Caffeine accelerates the motility of the large intestine. For some athletes this is a 'useful' effect before a start, but for people with diarrhea-predominant IBS it is a problem. Magnesium supplements, which are often taken for cramps, in the form of citrate or oxide have a laxative effect.

Drugs that affect the symptoms

Antibiotics are one of the best-known factors in microbiota changes. After a course of antibiotics, intestinal symptoms appear or intensify in some people. This is not a reason to refuse necessary treatment, but a reason to tell the doctor about IBS.

NSAIDs, which athletes often take for pain, increase the permeability of the intestinal wall and can worsen mucosal damage during prolonged loads. In people with IBS they can increase discomfort.

Other well-known drugs that affect motility are opioid analgesics (constipation), iron preparations (constipation or diarrhea), metformin (diarrhea) and some antidepressants. If these agents have been prescribed by a doctor, only the doctor can adjust them.

In the context of sports pharmacology, gastrointestinal symptoms are often described in users of stimulants and fat burners, as well as against the background of sharp dietary manipulations and diuretics. The editors emphasize that the non-medical use of such agents creates risks that far exceed intestinal discomfort.

Editors' conclusions

IBS is a chronic disorder of the 'brain-gut' interaction, and sport can both ease and aggravate its course. Moderate activity is usually beneficial, whereas prolonged intense work, heat and stress provoke symptoms.

Sports nutrition contains several typical triggers: sugar alcohols, lactose, excess fructose, caffeine and laxative forms of magnesium. Identifying individual triggers often yields more than general prohibitions.

Antibiotics, NSAIDs and a number of other drugs also affect the gut, so any changes in therapy should be discussed with a doctor.

We also recommend reading our materials on the prevention and diagnosis of IBS, on gastritis in athletes and on choosing a protein in case of lactose intolerance.

References

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