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Clark, Nancy M.S., R.D., CSSD, FACSM

ACSM's Health & Fitness Journal: May/June 2012 - Volume 16 - Issue 3 - p 22–26
doi: 10.1249/01.FIT.0000414752.46137.f4

LEARNING OBJECTIVES • To understand the types of exercise that are associated with gastrointestinal distress.

• To recognize medical issues that might contribute to exercise-associated diarrhea.

• To be able to advise athletes on ways to manage exercise-associated diarrhea.

Exercise-associated diarrhea afflicts an estimated 30% to 50% of athletes, particularly those who exercise at a high intensity in running-type sports. Athletes with a history of gastrointestinal problems (including irritable bowel syndrome, celiac disease, and lactose intolerance) are predisposed to this problem. While solutions to exercise-associated diarrhea are personal to each athlete, this feature offers guidelines that might provide some relief.

Nancy Clark, M.S., R.D., CSSD, FACSM, is a Boston-area sports nutrition counselor, workshop leader, and author of Nancy Clark’s Sports Nutrition Guidebook, 4th Edition. Her private practice is in Newton, MA.

Disclosure: The author declares no conflict of interest and does not have any financial disclosures.



Whether you call it urgency to defecate, diarrhea, or runners’ trots, an estimated 30% to 50% of athletes in running sports are afflicted by gastrointestinal (GI) problems that can leave them distressed or on the sideline (3). In most cases, exercise-induced diarrhea is just a major inconvenience, but in extreme cases, it can involve serious blood loss in the feces. The following guidelines can help athletes determine the cause of the problem and resolve the concern.

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Many athletes are involved in sports that require running, jumping, or movements that jostle the intestines. This can contribute to increased mechanical distress, particularly when exercise is performed at high intensity and for a long period, as happens during a marathon or triathlon. Runners have almost twice the symptoms of swimmers, cyclists, or other athletes, and elite athletes (as opposed to recreational exercisers) report 1.3 to 3 times more problems (3). Other factors that can increase intestinal motility include the following:







  • exercise-induced changes in intestinal hormones that hasten transit time
  • altered absorption rate. High concentrations of carbohydrate that create a high osmotic load can cause water to flow into the intestines to dilute the solution.
  • dehydration, with body weight loss of more than 4%
  • feelings of anxiety and stress, as commonly happens with preevent jitters
  • being a younger athlete or novice exerciser, with an untrained body that is not yet unaccustomed to the stress of exercise (and perhaps lack of knowledge about appropriate preexercise eating)
  • being female, particularly at the time of the menstrual period
  • having mild food intolerances (such as lactose intolerance) that might be dormant when at rest but get aggravated during hard exercise, as the gut becomes more sensitive
  • having preexisting bowel problems, such as celiac disease or irritable bowel syndrome (IBS). An estimated 10% to 20% of people in the United States have IBS (2).
  • Reduced blood flow to the intestines as the body sends more blood to the exercising muscles had been thought to contribute to diarrhea, but this theory has recently been challenged (6).
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Dehydration is a common contributor to the fecal urgency that happens toward the end of a long bout of exercise. Athletes who lose more than 4% of their body weight in sweat — that’s 6 lbs (3 kg) for a 150-lb (70 kg) athlete — may find themselves searching for a porta-toilet (3). Yet the very same athletes who experience diarrhea during extended exercise may try to drink as little as possible during exercise, thinking water or sports drink trigger GI problems. When they do succumb to drinking because of extreme thirst, they might experience coincidentally the urge to defecate.

Endurance athletes can resolve dehydration-associated diarrhea by learning their sweat rate, done by weighing themselves with minimal clothing before and after exercise, taking into account all fluids consumed during the exercise session. Each 1-lb (0.5 kg) drop in weight relates to a 1-lb (16 oz) loss of unreplaced sweat. Because athletes may sweat more in the summer heat, they should monitor sweat losses in differing seasons.

By practicing drinking the amount of fluid that matches sweat losses, the body can adjust during training to tolerating the proper fluid intake. Athletes might discover that preventing dehydration (by drinking earlier during events) resolves the problem — to say nothing of enhances their performance and shortens their recovery!

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Some athletes complain about GI problems associated with commercial sports foods such as gels. These products contain concentrated amounts of sugar that, for some athletes, contribute to fecal urgency. A study with runners during a 16-km (10 mile) race suggests 88% of them tolerated up to 90 g of carbohydrate (360 calories) per hour. But a few runners experienced severe GI distress, in particular, those who had a history of recurrent intestinal distress. This suggests that tolerance to gels might be unrelated to the gels, per se, but to any nutrient intake (4).

This is just one example of why, during training, athletes should practice consuming the foods or fluids they plan to consume during an endurance event such as a marathon or triathlon. They can learn which products settle well and may opt for fueling with commonly consumed foods to which their bodies are accustomed (gummi candies, dried fruit, etc.). Each athlete needs to find the balance of how to provide adequate fluid and carbohydrate to the working muscles, without creating intestinal distress.

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Although the intestinal jostling associated with running is a major risk factor for contributing to fecal urgency, an athlete’s daily training diet also can exacerbate the problem. Because food takes about 1 to 3 days to move through the intestinal tract, what an athlete eats on the days leading up to an event can contribute to GI problems. That’s why athletes want to consume “tried and true” preexercise foods and also why many elite athletes use their own electrolyte replacement bottles during competitive events.

Some common preexercise dietary triggers include the following:

  • Fiber. Triathletes with a high fiber intake reported more GI complaints than those with a low fiber intake. Some diarrhea-prone athletes choose to reduce their fiber intake for 1 to 3 days before competition. See Table (Fiber in Sports Foods) to learn which foods to limit.
  • Sorbitol. Sugar-free gum, candies, and breath mints that contain sorbitol (a type of sugar) can trigger diarrhea in some people who are sorbitol intolerant.
  • Coffee, tea, or other warm beverages. Hot fluids can stimulate gastric movement. Caffeine itself can have a laxative effect.
  • Fatty foods. Fried foods, burgers, spare ribs, and other greasy foods can contribute to diarrhea in athletes who have trouble digesting high-fat foods.
  • Spicy foods might cause problems in certain athletes, particularly if they cause problems at nonexercise times.
  • Alcohol, in significant amounts.
  • Vitamin C supplements, if taken in high doses.


To determine if exercise-induced diarrhea is connected to diet, athletes can track suspected food triggers by recording their food intake and fecal output. If the athlete suspects a specific food contributes to diarrhea, he or she can do an elimination diet followed by a food challenge. For example, if the athlete suspects the loose stools are related to enjoying bran cereal every day for breakfast, he or she could follow this protocol:

  1. Eliminate the suspected food for a week and observe any changes in bowel movements.
  2. Consume a double dose of the suspected food (a larger bowl of bran cereal) and observe any changes.

If the athlete stops experiencing fecal urgency during exercise when he or she reduces the intake of bran cereal but has a lot of trouble during a long run after having eaten a large bowl of bran cereal, the answer becomes obvious: consume less bran cereal!

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Lactose Intolerance

Some athletes, particularly African Americans, have trouble digesting lactose, the sugar that naturally occurs in milk. Athletes who are lactose intolerant can experience gas, bloating, and diarrhea. The solution is to switch to lactose-free milk (such as LactAid Milk), take LactAid pills with lactose-containing meals, or drink soymilk. Lactose-containing foods include those made with milk (pudding, creamy soups, ice cream) or soft cheese (pizza, grilled cheese sandwich made with American cheese).



Lactose-intolerant athletes who eliminate dairy foods need to be educated on how to consume alternate sources of calcium. Lactose-free calcium options include (preferably low fat) hard cheeses (low-fat cheddar and Swiss cheese), yogurt, calcium-fortified orange juice, and soy milk. Given that milk is one of the best sources of both calcium and vitamin D, athletes who do not drink milk may need to take supplements to boost their calcium intake to the recommended 1,000 mg per day for adults and 1,300 mg/day for teens, as well as vitamin D supplements (600 IU D2 or D3 per day).

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Celiac Disease

Celiac disease is caused by an autoimmune response to gluten, a protein found in wheat, barley, and rye. Athletes with celiac disease commonly experience diarrhea (or the opposite problem, constipation). Approximately 1% of the general population has celiac disease. Another 6% of the population has nonceliac gluten sensitivity with similar symptoms (but without the autoimmune reactions that can contribute to cancer and osteoporosis) (1). This means intestinal problems in at least 7% of athletes could be related to gluten intake.

Gluten-free diets are difficult to sustain, so athletes with persistent and unresolved GI problems who believe they are gluten intolerant should not self-impose a gluten-free diet without first talking with a physician who specializes in celiac disease. They should not eliminate gluten before getting tested for celiac disease because absence of gluten in the diet can interfere with making the correct diagnosis.

If athletes with suspected celiac disease don’t make the effort to get properly tested, they might miss a correct diagnosis — or diagnosis of other health problems, like Crohn’s, an ulcer, or colon cancer. Plus, if undiagnosed, they might be less motivated to strictly follow a gluten-free diet for life. This can result in anemia, stress fractures, cancer, osteoporosis, diabetes, and other autoimmune disorders. (For more information about celiac disease and gluten intolerance, see

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Irritable Bowel Syndrome

Although the exact cause of IBS is unknown, two aggravators include stress and diet. Some researchers suggest people with IBS have a colon that is very sensitive to certain foods and stress. Hence, athletes with IBS may be more susceptible to experiencing diarrhea. Athletes with IBS should try to eat even-sized meals on a regular schedule — an eating style that can be difficult to fit into a busy day. (For more information about IBS, see and, the International Foundation for Functional Gastrointestinal Disorders.).

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When all efforts to resolve exercise-associated diarrhea have failed, the athlete might want to consult with his or her physician about taking antidiarrhea medicine (such as Imodium or Lomotil) 1 hour before the athletic event. With medical guidance and monitoring, this remedy (used for special events but not on a daily basis) has helped keep some athletes in the game.



Lesli Bonci, registered dietitian of the University of Pittsburgh Medical Center recommends Certo or SurGel as an antidiarrhea option. They are pectins (used with making jam and jelly). A tablespoon mixed in water an hour before exercise can have a binding effect.

Although some athletes may be tempted to experiment with laxatives or colonic irrigation, they should be discouraged from doing so. Laxative use can become a “slippery slope” that borderlines on purging behaviors associated with eating disorders. Athletes should seek medical guidance and supervision regarding any purgative use.

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Many athletes are too embarrassed to seek help for their struggles with exercise-associated diarrhea. They need to know that “runner’s trots” are a common problem; they are not alone with their concerns. Because each person’s body is unique, each athlete needs to experiment with the timing and amount of different preexercise and during-exercise foods to find a solution that brings peacefulness to their exercise program.

  • Do make sure to be well hydrated before and during endurance exercise.
  • Do systematically eliminate foods from the diet to isolate suspected culprits.
  • Do experiment during training with commercial sports foods and fluids taken during exercise to learn their effects on the athlete’s intestinal tract.
  • Don’t draw conclusions about the presence of medical conditions, such as celiac disease, lactose intolerance, irritable bowel syndrome, or other GI problem, without seeking the services of a specialist in GI disease.
  • Don’t take antidiarrheal drugs without the advice of a sports medicine physician.
  • Don’t experiment with over-the-counter laxatives or colonic irrigation, and so on, without professional input and monitoring, for purposes of remaining objective about what could become an unhealthy crutch for an athlete with eating disorder.
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Exercise-associated diarrhea afflicts an estimated 30% to 50% of athletes, particularly those who exercise at a high intensity in running-type sports. Athletes with a history of GI problems (including irritable bowel syndrome, celiac disease, and lactose intolerance) are predisposed to this problem. Solutions to exercise-associated diarrhea are personal to each athlete; hence experimenting with pre-event fueling should be incorporated into the training program.

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1. Biesiekierski JR, Newnham ED, Irving PM, et al.. Gluten causes gastrointestinal symptoms in subjects without celiac disease: a double-blind randomized placebo-controlled trial. Am J Gastroenterol. 2011; 106 (3): 508–14.
2. Chey WD, Cash BD. Irritable bowel syndrome: update on colonic neuromuscular dysfunction and treatment. Curr Gastroenterol Rep. 2006; 8 (4): 273–81.
3. de Oliveira EP, Burini RC. The impact of physical exercise on the gastrointestinal tract. Curr Opin Clin Nutr Metab Care. 2009; 12 (5): 533–8.
4. Pfeiffer B, Cotterill A, Grathwohl D, Stellingwerff T, Jeukendrup A. The effect of carbohydrate gels on gastrointestinal tolerance during a 16-km run. Int J Sport Nutr Exerc Metab. 2009; 19: 485–503.
5. Winett RA, Carpinelli RN. Potential health-related benefits of resistance training. Prev Med. 2001; 33 (5): 503–13.
6. Wright H, Collins M, Villers RD, Schwellnus MP. Are splanchnic hemodynamics related to the development of gastrointestinal symptoms in ironman triathletes? A prospective cohort study. Clin J Sport Med. 2011; 21 (4): 337–43.

Gastrointestinal Distress; Runner’s Trots; Urge to Defecate During Exercise; Exercise-Induced Diarrhea; Digestive Problems in Athletes

© 2012 American College of Sports Medicine.