Runner’s diarrhea (EIGD) is a common issue affecting distance runners, involving frequent, loose bowel movements or urgency during or immediately following a run. Contributing factors include the physical jostling of the organs, reduced blood flow to the intestines during intense exercise, and the consumption of certain foods and fluids. Preventing this condition requires a strategic approach focusing on diet, hydration, training adjustments, and medical support.
Immediate Pre-Run Dietary Strategies
Managing what you consume in the 12 to 24 hours before a run is effective in preventing EIGD. High-fiber foods, such as whole grains, raw vegetables, bran, and beans, speed up intestinal transit time and should be limited or avoided the day before and the morning of a run.
Limiting high-fat foods is advisable, as fat takes longer to digest and remains in the intestines for extended periods. Certain carbohydrates can also be problematic. Sugar alcohols (like sorbitol and isomalt) and high-fructose corn syrup draw water into the intestines, leading to diarrhea. Avoiding these sweeteners, along with caffeine, which stimulates bowel movements, reduces the risk of symptoms.
The timing of your last solid meal ensures the stomach is mostly empty at the start of exercise. Consume your main pre-run meal two to four hours before your run, focusing on easily digestible, low-residue carbohydrates like white rice, bananas, or plain pasta. Any smaller, carbohydrate-rich snack consumed 30 to 60 minutes before should be low in both fat and fiber.
Hydration Timing and Composition
Proper fluid management is necessary, as both dehydration and overhydration contribute to gastrointestinal distress. Maintaining optimal hydration protects the gut lining and helps prevent intestinal permeability during intense exercise. Hydrate consistently in the days leading up to a run rather than consuming a large volume of fluid right before starting, which can cause stomach sloshing and discomfort.
The composition of fluids consumed during a run impacts gut stability. Highly concentrated carbohydrate solutions have a high osmolarity that can draw excess water into the gut and trigger diarrhea. Opting for hypotonic or isotonic solutions, or using multiple transportable carbohydrates (like a glucose-fructose blend) instead of glucose alone, may improve absorption and tolerance. Avoid consuming warm liquids, as these may accelerate the movement of food through the digestive tract.
Adjusting Running Intensity and Schedule
The mechanical and physiological stress of running is a major contributor to EIGD. During high-intensity running, the body redirects blood flow away from the gut to the working muscles, a process called splanchnic hypoperfusion. This temporary lack of oxygen and nutrients can compromise the intestinal barrier and cause symptoms.
Moderate your pace, especially during the initial miles of a run or during intense training. Slowing down or incorporating walking breaks helps redistribute blood flow back to the digestive system, reducing intestinal stress. You can “train the gut” by gradually introducing small amounts of race-day nutrition—gels or chews—during training runs, allowing the digestive system to adapt to processing fuel while active.
Medical and Supplemental Options
For runners who continue to struggle despite dietary and training modifications, non-lifestyle interventions can be considered. Over-the-counter anti-motility medications, such as loperamide (Imodium), can be used strategically to slow intestinal transit. This medication is reserved for race day or long, intense efforts where symptoms are predictable and severe.
Use these anti-motility agents cautiously, as they can interfere with nutrient absorption and fluid balance. Consulting with a healthcare provider is advised before incorporating them into a routine. Specific probiotics and prebiotics may support long-term gut health, helping to manage symptoms by promoting a stable gut microbiome.