Causes and solutions for runners' intestinal concerns

Row of portable toilets

"More marathons are won or lost in the porta-toilets than at the dinner table" proclaimed marathon king Bill Rodgers while talking to a group of runners.

You can fully understand the truth in that statement if you're among the many athletes who worry about unwanted pit stops, abdominal cramps or diarrhea. Transit troubles and gastrointestinal (GI) concerns are surprisingly common among both athletes and non-athletes alike.

  • An estimated 30 to 50 percent of distance runners experience intestinal problems related to exercise.
  • The vast majority (83 percent) of 471 marathoners who completed a survey reported they suffered GI problems occasionally or frequently during or after running: 53 percent experienced the urge to have a bowel movement and 38 percent reported diarrhea. Women were more likely than men to experience these problems.
  • Among 155 mountain marathoners, 24 percent had intestinal symptoms; two dropped out due to GI troubles.
  • Dieters (including athletes -- and those with eating disorders) are more likely than non-dieters to report abdominal pain, bloating, diarrhea and constipation.
  • In a random survey of 2,500 Americans, 40 percent reported one or more digestive symptoms in the month prior to the interview: diarrhea (27 percent), abdominal pain (22 percent), bloating (16 percent). These problems were more prevalent than expected and more prevalent among women than men.
  • Given the above data, we need to acknowledge this fact: Bowel problems are a concern for many active people. Yet this topic is rarely discussed; few athletes feel comfortable discussing their dilemma with diarrhea. This article addresses this concern and hopefully can reduce your transit troubles.

Causes of "runners' trots"

Many physiological facts help explain why diarrhea is a concern for athletes, particularly athletes in running-type sports: "jostling" of the intestines; reduced blood flow to the intestines as the body diverts blood flow to the working muscles; changes in intestinal hormones; altered absorption; dehydration.

Add high-intensity exercise, stress, anxiety, pre-event jitters, and little wonder athletes -- particularly young and novice athletes whose bodies are yet unaccustomed to the stress of hard exercise -- fret about "nervous diarrhea."

Exercise -- specifically more exercise than your body is accustomed to doing -- increases intestinal activity. (Even strength training accelerates transit time from an average of 44 hours to 20 hours in healthy, untrained 60-year-old men).

As your body adjusts to exercise, you may resume standard bowel movements. But not always, as witnessed by the number of experienced runners who carry toilet paper with them during exercise, and also know the whereabouts of every public toilet on the route.


To help alleviate the problem, try exercising lightly before the event to help empty the bowels. Experiment with training at different times of the day. Visualize yourself exercising with no intestinal problems; the problem may resolve with a positive mindset and experience. Fuel wisely; the following nutrition tips might help reduce the symptoms:

  • Reduce your intake of high-fiber cereals. You don't need the roughage! Fiber increases fecal bulk and movement, thereby reducing transit time. Triathletes with a high fiber intake reported more GI complaints than those with a lower fiber intake.
  • Limit "sugar-free" foods such as sugar-free gum and hard candies that contain sorbitol. This type of sugar can cause diarrhea.
  • Keep a food and diarrhea chart to pinpoint food triggers. Take away any suspicious foods -- excessive intakes of juice, coffee, fresh fruits, raisins, dried fruits, beans, lentils, milk, high-fiber breads and cereals -- for a week and then eat a big portion. Observe changes in bowel movements. If you stop having diarrhea when you stop eating bran cereal (but have a worrisome situation when you eat an extra-large portion), the answer becomes obvious: Eat less bran cereal.
  • To find the food culprit, you may need to look carefully at your prior diet, because food moves through most people's intestines in one to three days. A simple way to learn your personal transit time is to eat sesame seeds, corn or beets -- foods that can be seen in feces.
  • Drink extra water to maintain hydration. GI complaints are common in runners who have sweated off more than four percent of their body weight. (That's six pounds for a 150-pound athlete.) These same runners often believe the ingestion of fluid causes the diarrhea. The truth is the dehydration that occurs due to inadequate fluid intake is the true culprit.
  • When all else fails, you might want to consult with your doctor about occasionally using an anti-diarrhea medicine (such as Imodium). This may have side effects that hinder performance; be educated.
  • The bottom line (so to speak): You are not alone with your concerns. By experimenting with different food and exercise patterns, you may find a welcome solution.

Sports dietitian Nancy Clark, M.S., R.D., counsels casual and competitive athletes at Healthworks, the premier fitness center in Chestnut Hill, MA (617-383-6100). Her best-selling Nancy Clark's Sports Nutrition Guidebook, Food Guide for Marathoners and The Cyclist's Food Guide are available at

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