Gastrointestinal (GI) Concerns

Contributed by Dr. Steven T. Devor – Director of Performance Physiology for MIT and OhioHealth, and Associate Professor of Exercise Physiology, Department of Human Sciences, and Department of Physiology and Cell Biology, The Ohio State University

Gastrointestinal (GI) concerns is a problem that many runners and other endurance athletes have at one time or another. There are several reasons why you experience this sort of intestinal distress during and immediately after activity, and I believe some good strategies to minimize or even eliminate it from happening any longer are available.  Believe it or not, transit troubles and GI concerns are surprisingly common among both athletes and non-athletes alike. Consider the following facts I have culled from some recent research articles on the topic:
  • An estimated 30% to 50% of distance runners experience intestinal problems related to exercise.
  • The majority (approximately 83 percent) of 471 marathoners who completed a random survey after a major city marathon reported they suffered GI problems occasionally or frequently during or after running.  Additionally, 53% experienced the urge to have a bowel movement and 38% reported diarrhea.  It seems that the problems impact women were more than men.
  • Among 155 mountain marathoners that participated in another random survey following a different major city marathon, 24% had intestinal symptoms; two dropped out due to GI troubles.
  • People on a diet or those that are severely restricting caloric intake (including endurance athletes) are more likely than non-dieters to report abdominal pain, bloating, diarrhea, and constipation.
Given the above, it is clear that bowel problems are a concern for many active people.  Although this topic is rarely discussed due to the fact that many athletes are not comfortable discussing their dilemma with diarrhea.  Hopefully I can provide you with some strategies to reduce your transit troubles.

Many physiological forces come into play when trying to explain why diarrhea is a concern for endurance athletes and often particularly runners:  a.) “jostling” of the intestines during the activity; b.) reduced blood flow to the intestines during exercise as the body diverts blood flow to the working muscles for exercise; c.) changes in intestinal hormones during exercise; d.) absorption of food is altered during exercise; and e.) dehydration due to heavy sweating.  Add the high-intensity exercise of a race or hard workout, stress, anxiety, pre-race nervousness, and it is no surprise, particularly for inexperienced athletes whose bodies are yet unaccustomed to the stress of hard exercise, become concerned about “nervous diarrhea.”

Exercise, specifically more exercise than your body is accustomed to doing, greatly increases intestinal activity.  As your body adjusts to the amount and intensity of your exercise, you may resume standard bowel movements.  However this is not always true, as witnessed by the number of experienced runners who may carry toilet paper with them during exercise, and also know all of the public restrooms on their favorite running routes.

To help control the problem, try a solid warmup before a race to help empty the bowels.  Experiment with training at different times of the day.  Fuel wisely. For example:
  • Reduce your intake of high-fiber cereals the day before your race or hard workout.  You do not need the extra nutritional roughage.  Fiber increases fecal bulk and movement, thereby reducing transit time.  In a recent paper, triathletes with a high fiber intake reported more GI complaints than those with a lower fiber intake.
  • Limit “sugar-free” foods as much as possible.  Many of these foods such as sugar free gum and hard candies contain sorbitol as a sweetener.  This type of sugar can directly cause diarrhea.
To find the food(s) that cause the distress, you may need to look carefully at your diet.  Food moves through your intestines in one to three days.  A simple way to learn your personal transit time is to eat sesame seeds, corn, or beets, as these foods can be observed 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 is approximately six pounds on a 150 pound athlete).  Many endurance athletes often believe the ingestion of fluid causes the diarrhea.  The fact is the dehydration that occurs due to inadequate fluid intake is the source of the GI upset and diarrhea.
When all else fails, you might want to consult with your physician about occasionally using an anti-diarrhea medicine (e.g., Imodium).  This drug may have side effects that hinder performance so be educated.

Rest assured you are not alone with this issue. I would experiment with different nutritional choices and perhaps training patterns, and you will likely find the right solution for your GI problem.
Best wishes for your continued training success.
Dr. Devor

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