Why Runners Get GI Problems—and How to Reduce Them

Running can cause symptoms such as diarrhea, nausea, bloating, and abdominal discomfort.
Prolonged or intense exercise can disrupt normal gastrointestinal function. Runners may experience symptoms because blood flow is redirected toward working muscles and because exercise can affect gastrointestinal motility and intestinal integrity.

Hydration and carbohydrate intake matter.
Adequate carbohydrate intake and maintaining hydration before and during exercise are among the strategies with relatively consistent evidence for reducing exercise-associated GI problems.

“Gut training” can improve an athlete's ability to tolerate fueling.
Rather than waiting until race day to consume large amounts of carbohydrate, athletes can gradually practice their race-day fueling during training. Repeated exposure can help athletes adapt to the amount and type of food or carbohydrate they plan to consume during competition.