Runner’s diarrhea, often called “runner’s trots,” is a form of exercise-induced gastrointestinal distress (EIGID) characterized by frequent, loose bowel movements and urgency during or immediately following a run. This condition is common, affecting a large percentage of endurance athletes and significantly disrupting training and race performance. While the exact cause involves a complex interplay of reduced blood flow to the gut, mechanical jostling, and hormonal changes, understanding the steps available to mitigate these symptoms is the first step toward reclaiming comfortable, consistent running.
Immediate Pre-Run Fueling Adjustments
Dietary choices in the 24 hours leading up to a run significantly influence the likelihood of experiencing digestive distress. Foods that are high in fiber, such as bran, raw vegetables, and beans, should be severely limited. These high-residue foods increase the volume and water content of stool, which speeds up intestinal transit time and contributes to urgency.
High-fat foods slow down gastric emptying, increasing the chance of discomfort during physical activity. Caffeine acts as a strong gut stimulant and should be significantly reduced in the three to six hours before a run. For those with sensitivities, dairy products and artificial sweeteners, specifically sugar alcohols like sorbitol and xylitol, can trigger a laxative effect and should be excluded from the pre-run fueling plan.
Instead, the focus should shift to easily digestible, low-residue carbohydrates consumed in the hours before exercise. Options such as white rice, refined bread, bananas, or plain boiled potatoes provide readily available energy with minimal stress on the digestive system. A small, simple meal should be consumed roughly two to three hours before the run, allowing sufficient time for initial digestion without leaving the stomach completely empty.
Strategic Hydration Management
Both dehydration and overhydration can exacerbate gut symptoms. When a runner becomes dehydrated, the body’s blood volume decreases, which compounds the issue of blood being shunted away from the digestive tract to the working muscles. This reduced blood flow can make the intestinal lining more sensitive and less efficient at absorbing nutrients and fluid.
Conversely, consuming large volumes of fluid immediately before a run can lead to a feeling of sloshing and increase pressure within the gut, causing discomfort and urgency. The recommended strategy involves sipping fluids gradually in the hours leading up to the run, rather than gulping a large amount all at once. This approach ensures the body starts the run in a hydrated state without overloading the stomach.
The composition and temperature of fluids also play a role in gut comfort. Extremely cold or warm liquids can sometimes stimulate gut motility and should be avoided in favor of room-temperature beverages. For fluids consumed during the run, it is often best to utilize isotonic sports drinks, which have a carbohydrate concentration (typically 6-8%) that promotes rapid fluid and energy absorption without drawing excessive water into the intestine like hypertonic, sugary drinks can.
Training and Mechanical Considerations
Beyond diet and hydration, the physical act of running itself places unique mechanical and physiological stress on the gastrointestinal system. The repetitive, high-impact motion of running physically jostles the abdominal organs, which can contribute to the urgency and discomfort commonly associated with EIGID. Runners can manage this mechanical stress by ensuring their running attire is comfortable and not constricting around the waist, which can place additional pressure on the abdomen.
The intensity of a run directly correlates with the severity of gut symptoms, as harder efforts divert a greater percentage of blood flow away from the intestines. Starting a run with a gentle warm-up may help the body manage the necessary blood flow redistribution more gradually than an abrupt start. Pacing strategies that avoid excessive intensity, especially early in a run, can help maintain some blood flow to the gut and reduce digestive shock.
Anxiety and pre-race stress also influence the digestive system through the gut-brain axis, potentially increasing intestinal motility. Implementing routine stress-management techniques, such as mindful breathing or visualization, can help calm the nervous system and indirectly support gut function. Consistency in training volume, avoiding sudden spikes, also allows the gut time to adapt to the physical demands of running.
When Lifestyle Adjustments Are Insufficient
For runners who have optimized their fueling, hydration, and training yet continue to face significant issues, medical intervention may be considered. Over-the-counter anti-motility medications, such as loperamide (Imodium), can be used strategically to slow intestinal movement and should be tested in training before a race. This medication should only be used occasionally, as a temporary fix, and should never be relied upon as a daily solution.
Runners should seek professional medical evaluation if they experience persistent symptoms that do not resolve after two to three days or if diarrhea occurs even on non-running days. Symptoms requiring consultation include seeing blood in the stool, unexplained weight loss, or signs of severe dehydration. A sports dietitian or gastroenterologist can help identify underlying conditions or specific food triggers, such as nonsteroidal anti-inflammatory drugs (NSAIDs) or certain food intolerances, that may be contributing to the problem.