Exercise-Induced Gastrointestinal Syndrome (EIGS) describes the digestive disturbances that occur during or immediately after physical activity. Symptoms like diarrhea, abdominal cramping, and nausea are common, especially among endurance athletes, but they can affect any exerciser engaging in intense or prolonged workouts. This condition is a physiological response to stress, with studies suggesting that between 30% and 90% of athletes experience some form of EIGS. While often benign, the sudden need for a restroom break can negatively impact training or competition performance.
The Physiological Reasons Exercise Causes Digestive Issues
The body prioritizes supplying blood to the working muscles, a process that severely restricts blood flow to the gut. During intense exercise, the blood supply to the splanchnic circulation, which includes the stomach and intestines, can be reduced by up to 80%. This temporary lack of blood flow is called splanchnic hypoperfusion, and it can cause the intestinal lining to become damaged and more permeable. The resulting “leaky gut” allows substances to pass through the intestinal barrier, leading to irritation and rapid movement of contents through the digestive tract.
Physical motion, particularly the repetitive jarring experienced in high-impact activities like running, acts as a mechanical stimulant to the bowels. This jostling increases gut motility, accelerating the transit time of food and waste, which leaves less time for water absorption. Reduced water absorption results in looser, more urgent stools.
Hormonal changes also play a role in this digestive disruption. Intense physical exertion triggers the release of stress hormones, known as catecholamines, into the bloodstream. These hormones, which include epinephrine and norepinephrine, contribute to the fight-or-flight response that speeds up the movement of the gut. The combination of reduced blood flow, mechanical trauma, and hormonal stimulation overwhelms the digestive system, leading directly to post-exercise diarrhea.
Nutritional and Timing Adjustments Before Exercise
Preventative nutrition focuses on minimizing stress on the gut before the workout. The most effective approach involves limiting or avoiding foods that are slow to digest or that draw excess water into the intestines. Foods high in fat, protein, and fiber should be reduced for at least two to four hours prior to exercise. These macronutrients take longer to process, increasing the likelihood of symptoms.
Many exercisers benefit from adopting a low-FODMAP diet in the 24 hours leading up to a strenuous effort. FODMAPs, which are fermentable carbohydrates, are poorly absorbed and can cause osmotic diarrhea by pulling water into the colon. Avoiding items with high concentrations of fructose, lactose, and artificial sweeteners like sorbitol and mannitol can significantly reduce the risk of distress.
The timing of the last meal is also a significant factor in prevention. Large, solid meals should ideally be consumed at least three to four hours before exercise to allow for proper gastric emptying. If a small snack is necessary closer to the workout, select easily digestible, low-fiber carbohydrates, such as a plain banana or white rice, consumed 30 to 60 minutes beforehand.
Hydration must be balanced to support the body without overwhelming the gut. Avoid consuming hypertonic sports drinks—those with a very high concentration of carbohydrates—immediately before or during the activity. These solutions can delay gastric emptying and pull fluid into the intestines, worsening symptoms. Instead, focus on water or isotonic solutions containing a balanced mix of electrolytes and carbohydrates.
Managing Acute Symptoms and Post-Workout Recovery
If symptoms of diarrhea begin during a workout, the most effective immediate action is to stop or significantly reduce the intensity of the exercise. This allows blood flow to return to the splanchnic area, helping the gut lining recover and slowing down motility. For planned events where symptoms are a known risk, an over-the-counter anti-motility medication like loperamide can be used sparingly, but only after consulting a healthcare provider.
Post-workout recovery should center on gentle refeeding and the thorough replacement of lost fluids and electrolytes. Foods that are easy to digest, such as the components of the BRAT diet—bananas, rice, applesauce, and toast—can help firm up stools and provide necessary calories without irritating the gut. Replacing sodium and potassium is particularly important, as these electrolytes are lost through both sweat and diarrhea.
While most cases of exercise-induced diarrhea resolve quickly, certain red flag symptoms require medical attention. Persistent symptoms lasting longer than two days, signs of severe dehydration, or the presence of bloody stool indicate the need for a doctor’s consultation. These symptoms may signal a more serious underlying condition.