Irritable Bowel Syndrome in Athletes: Causes, Training Load and Medications

Cramping halfway through a long run, an urgent dash to the restroom before a race, bloating that makes heavy squats miserable: gut trouble is one of the most common and least discussed problems in sport. For some athletes, these symptoms are part of irritable bowel syndrome (IBS). Our editorial team reviewed how exercise, nutrition strategies and medications interact with this condition.

What IBS is, and what it is not

Irritable bowel syndrome is a disorder of gut-brain interaction. It causes recurrent abdominal pain associated with changes in bowel habits, either diarrhea, constipation or a mix of both. Under the Rome IV criteria, pain must occur on average at least one day per week over the last three months, with onset at least six months before diagnosis.

IBS does not damage the intestine or raise the risk of colon cancer. Standard tests usually come back normal. The problem lies in how the gut moves, how sensitive its nerves are, and how it communicates with the brain. Gut microbiota, previous infections and stress all appear to play a role.

It is common. Estimates suggest that around 5 to 10 percent of adults worldwide meet diagnostic criteria, with higher rates in women. Among athletes, exact prevalence is uncertain, but exercise-related gastrointestinal complaints are extremely frequent, particularly in endurance sports.

It is important to separate IBS from exercise-associated gastrointestinal symptoms that appear only during hard sessions. Many runners have so-called "runner's trots" without having IBS. The distinction matters because the management differs.

How exercise affects the gut

During intense exercise, blood flow is redirected away from the digestive tract toward working muscles and the skin. Splanchnic blood flow can fall substantially at high intensities. Costa and colleagues (2017) described this as part of "exercise-induced gastrointestinal syndrome," which includes reduced gut perfusion, increased intestinal permeability and altered motility.

Mechanical jostling adds to the problem. Running produces far more gut symptoms than cycling or swimming at similar intensity. Dehydration, heat and high carbohydrate intake during events can amplify discomfort, particularly in people whose gut is already sensitive.

Interestingly, moderate exercise helps IBS. A randomized trial by Johannesson and colleagues (2011) found that people with IBS who increased physical activity to 20 to 60 minutes of moderate to vigorous exercise three to five days a week had significantly greater symptom improvement than controls. The relationship therefore follows a curve rather than a straight line.

Psychological load matters as well. Competition anxiety, travel and disrupted sleep influence the gut-brain axis. Many athletes notice that symptoms flare in the days before a key race, even with unchanged diet.

Supplements and medications that can trigger symptoms

Sports nutrition products and common medications can either mimic or worsen IBS. Identifying these triggers is often the fastest route to relief, and it is one of the reasons a full history of everything an athlete takes is essential.

NSAIDs deserve special mention. Taking ibuprofen before endurance exercise has been shown in research to aggravate small intestinal injury. The habit of "pre-loading" painkillers before long events is common and should be discouraged.

Lactose in whey concentrate, inulin and chicory root fiber in "gut health" bars, and large doses of creatine taken all at once can also cause trouble in sensitive people. Switching to whey isolate or splitting doses often helps.

Performance-enhancing drugs are rarely discussed in this context, but stimulant-based fat burners and certain oral compounds are reported to cause gastrointestinal distress. They also carry far greater health risks than any gut symptom, which is another reason to avoid them.

Diagnosis and red flags

IBS is a positive diagnosis based on symptoms, but a doctor will usually exclude other conditions first. The American College of Gastroenterology guideline (Lacy et al., 2021) recommends testing for celiac disease in people with diarrhea-predominant symptoms and considering fecal calprotectin or C-reactive protein to screen for inflammatory bowel disease.

Athletes need careful evaluation because some features overlap with relative energy deficiency in sport, eating disorders, iron deficiency and thyroid problems. A sports medicine physician or gastroenterologist is the right first stop.

• Blood in stool or black, tarry stools
• Unintentional weight loss
• Symptoms waking you from sleep
• Onset after age 45 or a family history of colon cancer, celiac disease or IBD
• Fever, anemia or persistent vomiting

Any of these warning signs calls for prompt medical assessment rather than self-management. They are not typical of IBS and may point to another condition.

Managing IBS without giving up training

The low-FODMAP diet has the strongest dietary evidence. Halmos and colleagues (2014) showed in a controlled crossover trial that a low-FODMAP diet reduced IBS symptoms compared with a typical Australian diet. It should be done in phases, with elimination followed by systematic reintroduction, ideally with a registered dietitian.

Gut training is a practical tool for endurance athletes. Gradually practicing race-day carbohydrate intake during training appears to improve tolerance. Testing new products in training rather than on race day is a basic but often ignored rule.

Timing matters too. Many athletes do better with a lower-fiber, lower-fat meal three to four hours before competition, a stable pre-race routine and avoiding high-dose caffeine if it triggers urgency.

Medical options include soluble fiber such as psyllium, antispasmodics, peppermint oil, and prescription therapies chosen by a physician based on symptom pattern. Gut-directed cognitive behavioral therapy and hypnotherapy have good evidence and are underused in sport.

The Editorial Team's Conclusions

IBS in athletes sits at the intersection of training load, nutrition, psychology and medication use. Moderate exercise tends to help; very intense or prolonged efforts can provoke symptoms.

Many triggers are within the athlete's control: NSAIDs before exercise, sugar alcohols, concentrated sweeteners, large caffeine doses and untested race fuel.

A structured approach with medical evaluation, a low-FODMAP trial guided by a dietitian and gut training can allow most athletes to keep performing.

Related topics worth exploring include our guides to NSAIDs and tendon healing, to choosing a lactose-free protein, and to fueling strategies for long endurance events.

References

1. Lacy BE, Pimentel M, Brenner DM, et al. ACG clinical guideline: management of irritable bowel syndrome. Am J Gastroenterol. 2021;116(1):17–44.
2. Lacy BE, Mearin F, Chang L, et al. Bowel disorders. Gastroenterology. 2016;150(6):1393–1407.
3. Costa RJS, Snipe RMJ, Kitic CM, Gibson PR. Systematic review: exercise-induced gastrointestinal syndrome—implications for health and intestinal disease. Aliment Pharmacol Ther. 2017;46(3):246–265.
4. de Oliveira EP, Burini RC, Jeukendrup A. Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Med. 2014;44(Suppl 1):S79–S85.
5. Johannesson E, Simrén M, Strid H, et al. Physical activity improves symptoms in irritable bowel syndrome: a randomized controlled trial. Am J Gastroenterol. 2011;106(5):915–922.
6. Halmos EP, Power VA, Shepherd SJ, et al. A diet low in FODMAPs reduces symptoms of irritable bowel syndrome. Gastroenterology. 2014;146(1):67–75.