There is no single proven way to prevent runner’s diarrhea: food, fueling, hydration, heat, running duration and the jostling of exercise may all play a part, and individual responses differ. Keep your routine familiar, track when symptoms happen, and test one adjustment at a time during training rather than making untested changes on race day.
How can I prevent runner’s diarrhea?
Runner’s diarrhea means frequent, loose bowel movements during or immediately after a run, according to Mayo Clinic. Practical steps may help you identify and manage your own triggers, but evidence for specific prevention strategies is limited. Exercise-associated gut symptoms can have several contributors, including the physical demands of running, food and drink, and fueling choices.
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A 2025 joint position statement from Sports Dietitians Australia and the Ultra Sports Science Foundation recommends individualized assessment. It reports generally beneficial outcomes for maintaining appropriate hydration, carbohydrate and protein intake, selected FODMAP dietary adjustments, and gut training or feeding-tolerance changes, while noting that some interventions have uncertain or negative outcomes. These findings concern exercise-associated gastrointestinal symptoms broadly; they do not establish a guaranteed cure for runner’s diarrhea.
Find your own pattern before changing your diet
For a few runs, note what you ate and drank, when you had it, any fueling products used, the run’s duration and intensity, the weather, and when symptoms began. Look for repeatable associations rather than assuming that every commonly mentioned food is a problem. The 2025 position statement recommends individualized assessment because athletes’ symptoms and responses vary.
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Dietary avoidance is common, but it does not prove that a food causes symptoms or that avoiding it prevents diarrhea. In a 2020 questionnaire study of 388 runners, respondents reported avoiding meat (32%), milk products (31%), fish or seafood (28%), poultry (24%), and high-fiber foods (23%) before exercise. Those are reported behaviors, not evidence that the restrictions work. The study also found that diarrhea incidence increased with running distance.
Keep pre-run meals and race-day fueling familiar
Practice the meal, drinks, and fueling products you plan to use on race day in training. Mayo Clinic advises against trying a new energy gel or bar on race day. A familiar product may suit one runner and upset another, so use training runs to assess your tolerance.
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Longer runs can also require a practiced fueling plan. Gradually rehearse the amount and timing of food or sports products you expect to take in, instead of making a sudden change during a race. World Athletics identifies longer duration, heat, jostling, some foods and drinks, caffeine, nonsteroidal anti-inflammatory drugs (NSAIDs), and bicarbonate as potential risk factors for exercise-related gut symptoms; these factors do not affect every runner in the same way.
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Test meal timing and possible triggers
Mayo Clinic suggests experimenting with the timing and amount of food before a run, and with foods and drinks that may be associated with symptoms. These are practical options to test, not rules proven to prevent diarrhea in every runner.
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- High-fiber or gas-producing foods: If your notes suggest a connection, try limiting them during the preceding day and see whether the pattern changes.
- High-fat foods and caffeine: Mayo suggests testing whether limiting them in the three to six hours before a run helps you.
- Sugar alcohols: Check whether products containing them appear in your food or fueling routine when symptoms occur.
- FODMAP-containing foods: Responses vary. The focused review of runner’s diarrhea found no study linking FODMAPs to runner’s diarrhea in the evidence it examined. The broader 2025 position statement reports that FODMAP manipulation may help some exercise-associated symptoms in selected contexts; that is not a reason to adopt a long-term restrictive diet without individualized guidance.
Change one factor at a time where practical, while keeping other parts of your routine steady. That makes it easier to tell whether an adjustment is associated with a difference.
Hydrate appropriately and build feeding tolerance
Maintaining euhydration—appropriate hydration status—is supported by the 2025 joint position statement for managing exercise-associated gut symptoms. Mayo Clinic advises taking fluids before, during, and after running. The goal is appropriate hydration, not simply drinking as much as possible; the cited guidance does not establish that extra fluid alone prevents runner’s diarrhea.
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Gut training means gradually practicing the drinking and fueling routine you expect to use during longer or harder efforts, so you can assess how well you tolerate it. World Athletics also recommends rehearsing race nutrition in training. Make adjustments progressively and keep track of symptoms rather than treating a particular schedule or product as universal.
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Know when dietary restrictions are not the answer
A focused review of runner’s diarrhea describes possible ischemic, mechanical, and nutritional factors, but says evidence about causes and prevention remains limited. It found limited evidence that consuming multiple-transportable carbohydrates during exercise may help compared with glucose alone; this should not be treated as a proven diarrhea-prevention method.
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The same review found no evidence supporting a gluten-free diet as a way to prevent runner’s diarrhea in runners without celiac disease. Broadly cutting out foods can make it harder to meet fueling needs, so avoid eliminating whole food groups or starting a long-term low-FODMAP diet as a default fix. If symptoms persist or the problem is complex, an individualized plan from a healthcare professional or sports dietitian may be more useful than continued trial-and-error.
When to seek professional advice
Mayo Clinic advises consulting a healthcare provider if practical changes do not help. The available guidance does not establish a specific red-flag checklist for this article; if symptoms concern you, seek advice from a qualified healthcare professional rather than relying on dietary adjustments alone.
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