Runner’s diarrhea—loose, frequent bowel movements during or soon after a run—can result from several factors working together, including jostling, reduced blood flow to the gut during strenuous exercise, food and drink choices, and stress. A symptom diary can help you identify personal triggers, but blood in your stool, persistent diarrhea, or symptoms that do not improve with reasonable changes warrant medical advice.
Why do I get diarrhea when I run?
There is no single explanation for every runner. Mayo Clinic describes runner’s diarrhea as frequent, loose bowel movements during or immediately after running, and says it is most common in long-distance runners. Possible contributors include the physical jostling of running, reduced intestinal blood flow during strenuous effort, changes in intestinal hormone secretion, unfamiliar or increased food intake, and pre-race anxiety or stress. These are possible contributors, not a diagnosis of the cause in an individual runner.
Exercise-related gastrointestinal complaints are often grouped as physiological, mechanical, or nutritional. Intense exercise—particularly when a person is hypohydrated—can reduce blood flow to the intestines. Running’s repeated impact and what a runner eats and drinks can also matter. These factors may overlap; none proves that a particular episode is harmless or caused only by running. A 2014 review estimated that 30–50% of athletes report gastrointestinal complaints in studies generally. That estimate covers a range of GI complaints, not runner’s diarrhea alone, and the review notes that rates vary with the population, sport, intensity, conditions, and study methods.
How can you identify a trigger?
Rather than eliminating foods indiscriminately, keep a brief record of the factors around episodes. Individual responses vary, and the available evidence does not establish one prevention routine that works for everyone.
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- Record the run’s duration and intensity, and whether symptoms began during the run or afterward.
- Note what and when you ate, including fiber-rich or gas-producing foods and high-fat foods.
- Track caffeine, gels, bars, sports drinks, and other products, including whether they were new to you.
- Record fluid intake, signs that you may have been underhydrated, and stress or anxiety before the run.
Look for a pattern across more than one run before deciding a food or habit is a trigger. Change one low-risk factor at a time where practical, so you can tell what helps without unnecessarily restricting your diet.
What can you try before your next run?
Mayo Clinic offers practical suggestions to test against your own symptoms. These are not mandatory rules for every runner, and a change that helps one person may not help another.
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- Experiment with a fiber intake that you tolerate, and consider limiting high-fiber or gas-producing foods before running.
- Avoid sugar alcohols before a run, and consider limiting caffeine and high-fat foods in the hours beforehand.
- Try not to eat for a short period before running if eating close to a run seems to trigger symptoms.
- Drink fluids, and be cautious with energy gels and bars if they appear to contribute to symptoms.
- Avoid taking nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen, around exercise as a way to manage discomfort; they can increase gastrointestinal complaints. If you take regular medication, discuss any change with a clinician rather than stopping it on your own.
Do not test unfamiliar foods, gels, bars, or drinks on race day. If you are considering a change to fueling or hydration, try it during training and note how you respond.
What the evidence says about nutrition strategies
A 2025 joint position statement from Sports Dietitians Australia and the Ultra Sports Science Foundation identifies individualized assessment, hydration, carbohydrate and protein intake, dietary FODMAP manipulation, and gut training or adjustments to feeding tolerance as approaches with generally consistent beneficial outcomes for exercise-associated symptoms. That does not amount to a universal prescription or a recommended dose. FODMAP changes can be restrictive; seek suitable professional guidance rather than adopting a restrictive diet on your own.
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A 2017 review says research supporting proposed nutritional prevention strategies is limited. It does not support recommending a gluten-free diet to prevent exercise-induced diarrhea in athletes who do not have celiac disease. Neither a particular food schedule nor a specific product is established as a universal fix.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.When should you see a doctor?
Contact a health care provider if you see blood in your stool, have persistent diarrhea, or do not improve after reasonable practical changes. The International Foundation for Gastrointestinal Disorders advises bringing bleeding and persistent diarrhea to a doctor’s attention, and Mayo Clinic recommends consulting a health care provider if its prevention suggestions do not help.
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These signs are not a complete guide to every possible cause or emergency. If symptoms are severe or you feel acutely unwell, seek prompt professional assessment instead of trying to manage them on your own. Avoid treating antidiarrheal medicine as a routine solution without individualized advice from a health care professional.
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- HEALTHY & CONVENIENT HYDRATION: Include 2x 10oz/300ml NO RESIDUAL TASTE BPA-free Water Bottles, which apart from safe is also incredibly durable, You don't need to remove the cap in order to drink your water, this drinking bottle has a leakproof PUSH-PULL nozzle that allows you to enjoy your water even while you're on the move! TOP TIP, wash the flask out a few times before using.
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Sources
- Mayo Clinic Staff, “How can I prevent runner’s diarrhea?”, July 8, 2021.
- de Oliveira, Burini, and Jeukendrup, “Gastrointestinal Complaints During Exercise: Prevalence, Etiology, and Nutritional Recommendations,” Sports Medicine, May 3, 2014.
- de Oliveira, “Runner’s diarrhea: what is it, what causes it, and how can it be prevented?”, Current Opinion in Gastroenterology, January 2017.
- Costa et al., joint Sports Dietitians Australia and Ultra Sports Science Foundation position statement, Sports Medicine, April 7, 2025.
- International Foundation for Gastrointestinal Disorders, “Can Intense Exercise Lead to GI Symptoms?”
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