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Don't Miss Gastrointestinal Disorders in Athletes

Margot Putukian, MD with Carol Potera


In Brief: Gastrointestinal symptoms in physically active persons can be caused by gut ischemia, dehydration, the use of tobacco and alcohol, medications, and certain foods and fluids. Exercise may also unmask underlying medical problems, the more serious being inflammatory bowel disease, ulcers, and malignancy. Athletes often ignore or are reluctant to talk about symptoms, so physicians must ask specific questions. Diagnosis requires checking orthostatic blood pressure to detect dehydration and conducting a thorough physical examination. Laboratory tests may include a complete blood count, iron studies, thyroid and occult-blood tests, and stool cultures. Treatment may include simple dietary or exercise modifications or medications. Antidiarrheal medications, however, may cause troublesome central nervous system side effects.

Gastrointestinal (GI) problems are common among athletes. Exercise-related symptoms in the upper GI tract can include nausea, bloating, heartburn, and acid reflux; symptoms of the lower GI tract may include diarrhea, the urge to defecate, and rectal bleeding (1). Such symptoms are often seen as a natural result of sports participation and hard training, so an athlete may ignore symptoms and seek medical care only when they become severe enough to interfere with performance. Unfortunately, GI symptoms can signal more serious conditions, such as "food poisoning," inflammatory bowel disease, or cancer, and physicians must not assume that athletes are immune to these.

What kinds of GI problems occur in various sports?

When I review the literature with respect to GI problems in sports, there's not much available, and information about runners' diarrhea dominates. However, runners aren't the only athletes who have GI problems, and problems are not confined to the lower GI tract. A recent study (2) of GI complaints in recreational triathletes found that half reported upper GI symptoms like bloating and gas, and 27% had tested positive for occult stool blood. In a study of wrestlers, swimmers, and gymnasts (3), GI complaints occurred significantly more frequently among swimmers. A survey (1) of 700 runners revealed that 42% had occasional upper GI symptoms and that these occurred more often during and after hard runs than during and after easy runs. And in another survey (4), 58% of endurance athletes reported upper GI symptoms, and 61% reported lower GI symptoms.

What causes GI symptoms related to exercise?

Many factors are believed to play a role, but one major mechanism is gut ischemia. As the intensity of exercise rises, less blood flows to the viscera, and more flows to the working muscles. Exercising at 70% of VO2 max reduces blood flow to the GI tract by 60% to 70%. Because of the lack of blood flow and nutrients, cells in the viscera die and slough off and then show up as occult fecal blood or even bloody diarrhea. A number of studies have produced evidence of this effect. Among marathoners, 23% have occult blood loss (5), and heme-positive stools in cyclists correlated with hard training rides (6). In addition, endoscopic examination revealed ischemic lesions in runners' upper GI tracts after a long run (7).

Dehydration exacerbates gut ischemia and GI blood losses. Staying hydrated (see "Proper Hydration—Without Sloshing," below) during an endurance event may help prevent these conditions. In one study, 80% of runners who lost at least 4% of their body weight during exercise because of fluid losses experienced lower GI symptoms (8).

So we know that blood loss can be caused by dehydration and shunting of blood away from the viscera. Other causes include mechanical trauma of the GI tract from vibration, losses through the urinary tract, and heel-strike hemolysis. Exercise may also cause changes in the release of hormones such as pepsinogen and gastrin, and these changes may lead to GI symptoms. We need more information to understand the relationships among all of these factors.

Do sports drinks sometimes trigger GI problems?

Sport carbohydrate drinks can be a major culprit in producing GI side effects. Drinks with carbohydrate concentrations greater than 6% to 10% can cause diarrhea. The percentage of total carbohydrates is on the nutrition label. The old standbys, like Gatorade and All Sport, fall into the 6% to 10% range and should not cause problems. With higher concentrations, some athletes get a "dumping syndrome" because of fast osmotic changes in the GI tract. The wall of the GI tract acts as a semipermeable membrane, and water rushes in to dilute the concentrated sugar.

It's important to remember that every athlete is different, so some can tolerate a higher carbohydrate concentration than others. However, as exercise intensity changes, higher concentrations may no longer be tolerated.

Can food, caffeine, alcohol, or tobacco contribute to GI symptoms?

Eating foods with a high glycemic index (table 1: not shown) before exercise can also provoke diarrhea by increasing the osmotic load in the GI tract. The glycemic index, which was developed in 1981 as an aid to diabetics, ranks foods according to how quickly carbohydrates are absorbed and blood glucose levels rise after eating them (9). Athletes should avoid high-glycemic-index foods just prior to exercise because they speed transit through the GI tract. Low-glycemic foods, like power bars, some fruits, and yogurt, are preferable.

Caffeine acts as a laxative in some people and, because of its diuretic effect, can also contribute to dehydration. Athletes hear that caffeine prolongs endurance by sparing muscle glycogen and may load up on it. (See Nutrition Adviser, "Caffeine: A User's Guide." ) They don't realize that the caffeine they take in may be the reason they have diarrhea.

Alcohol and smoking are associated with a higher incidence of upper GI disorders, such as gastritis, acid reflux, ulcers, esophagitis, and stomach cancer. So the use or abuse of caffeine, alcohol, and cigarettes can be important in athletes with GI symptoms.

How do you approach history-taking with patients who complain of exercise-related GI symptoms?

Perhaps surprisingly, patients who come to the clinic suffering with GI symptoms are not always open about describing their problems. The more we ask patients about specific symptoms, the more problems we uncover. In fact, some active patients assume their condition is inevitable or incurable. All the articles about runner's diarrhea, for example, give a false idea that it's natural for runners to suffer from this condition. Sometimes athletes are embarrassed to report symptoms like bloody diarrhea. One athlete who suffered from bloody diarrhea was too embarrassed to tell his own father, who was a physician (see "Athletes With GI Symptoms: Two Case Reports," below). When he came to our clinic, I had to ask directly about bloody diarrhea before he admitted it was occurring.

What questions do you include in the history?

As with any medical problem, the history should focus on specific symptoms, when they occur, and specific precipitants. I ask the patient to describe specific symptoms, such as cramping, nausea, or bloating, and—to differentiate upper and lower GI problems—where the symptoms occur. I ask about when the symptoms occur in relation to exercise, and what the patient does when he or she has symptoms.

Other questions, such as those about weight loss, malaise, fever, and chills, relate to evidence of systemic disease. I ask about stress level and whether the patient gets nervous before or during competitive events, training, or both. I watch for a history of gastritis and ulcers, including aphthous mouth ulcers that are characteristic of inflammatory disease. If there is nausea accompanied by burning, it could indicate an ulcer, esophagitis, gastritis, or a tumor.

The medical history should also uncover information about a patient's use of caffeine, alcohol, tobacco, antibiotics, NSAIDs or other medications, sports drinks, and foods eaten prior to exercise.

Two classes of medications are particularly important to ask about: antibiotics and NSAIDs. Any type of antibiotic can cause diarrhea, and NSAIDs are associated with colonic bleeding, gastritis, ulcers, and diarrhea (10). Either of these types of medications can, in combination with exercise, lead to diarrhea. Erythromycin stands out as an antibiotic known for causing upper GI symptoms, especially stomach pain. Some antibiotics can result in pseudomembranous colitis or Clostridium difficile superinfection.

NSAIDs and aspirin can act as a direct irritant and result in gastritis, duodenitis, or ulceration. In addition, these medications, which many athletes use to decrease muscle soreness, can unmask more serious GI bleeding such as inflammatory bowel disease or malignancy.

Finally, a thorough history should always include questions about any family history of inflammatory bowel disease or GI malignancy.

What do you look for in the physical exam?

The initial physical exam is fairly straightforward. Physicians too often assume that athletes are "dehydrated" without a clinical confirmation. Checking orthostatic blood pressure helps to diagnose dehydration. Take the patient's blood pressure and heart rate after they have been supine for 10 minutes. Then have the patient stand for 5 minutes and repeat the measurements. A drop in systolic blood pressure of 20 points or an increase in heart rate of 20 points is consistent with dehydration and signals the need to look for the source of fluid losses.

The abdomen should be auscultated for bowel sounds and palpated for tenderness and abdominal mass. Rebound or guarding is not common, but it is a sign of significant pathology and should be carefully assessed. I also check for signs of an abnormal thyroid; hyperthyroidism can present as diarrhea, and hypothyroidism as constipation. In the remainder of the exam, I look for evidence of systemic disease that may have GI symptoms.

What lab tests are helpful in diagnosing GI conditions?

Deciding which tests to order (table 2) depends on the specific symptoms. If there's concern about GI blood loss, or if a patient has fatigue, diarrhea, or bloody stools, a complete blood count (CBC) helps confirm whether iron is being lost. In a patient with a history of fatigue and poor iron intake, I check serum iron, total iron-binding capacity, and ferritin along with the CBC to uncover iron deficiency. A test for occult blood should be performed to confirm GI blood loss. I always give an athlete with iron-deficiency anemia three Hemoccult cards to check for occult blood in their stools. Another option is to perform a rectal exam with a Hemoccult test.

Table 2. Initial Tests Used in the Diagnosis of Gastrointestinal Disease in Active Patients

Symptom or SignTests

Fatigue, diarrhea, bloody stoolOrthostatic blood pressure (take blood pressure and heart rate after patient is supine for 10 min and again after patient stands for 5 min; a 20-point drop in systolic pressure or a 20-point increase in heart rate suggests dehydration); complete blood count; fecal occult blood; thyroid stimulating hormone
Persistent diarrheaFecal leukocyte, fecal occult blood, stool sample culture, thyroid-stimulating hormone
Fatigue with history intakeComplete blood count, ferritin, of poor iron serum iron, total iron-binding capacity

Even in young, healthy athletes, it's important to determine how blood loss may be occurring. In particular, don't assume that iron-deficiency anemia in a female athlete is due to a poor iron intake and menstruation (see "Athletes With GI Symptoms: Two Case Reports," below). When the occult-blood test is positive and no obvious causes are present, referral to a gastroenterologist for further testing is warranted.

If a patient has persistent diarrhea, consider infectious agents, such as Salmonella, Shigella, Yersinia, or Campylobacter, and obtain a stool sample for cultures as well as fecal leukocytes. For patients who have been taking antibiotics, cultures should also be done for C difficile. Hypothyroidism and hyperthyroidism can cause GI symptoms, and therefore thyroid-stimulating hormone and thyroxine tests can also be helpful.

Although fairly simple, these tests rule out underlying medical problems that may be harbingers of serious illness and impair athletic performance.

What other conditions would you include in the differential diagnosis?

Probably the most important causes to consider are inflammatory bowel disease, ulcers, reflux esophagitis, and occult malignancy. Inflammatory bowel disease includes Crohn's disease and ulcerative colitis. Crohn's disease can affect the entire GI tract from the mouth to the anus, whereas ulcerative colitis is limited to the colon. Upper GI symptoms can include nausea, hematemesis, and abdominal pain, and lower GI symptoms can include cramping, diarrhea, and bloody stools.

Reflux esophagitis, gastritis, and ulcers can present with nausea, vomiting, heartburn, and abdominal pain, as well as hematemesis.

Occult malignancy can present with upper or lower GI symptoms, depending on location. Malignancy may be associated with weight loss, fatigue, malaise, and other constitutional symptoms.

How do you treat upper GI symptoms?

Modifying the diet can help (table 3). Alcohol, fatty foods, caffeine, and peppermint relax the esophageal sphincter, allowing stomach acid to reflux, which can be painful and produce nausea.

Table 3. Treatment of Common Exercise-Related Gastrointestinal (GI) Symptoms*

Symptom or SignTreatment

Heartburn, nausea, acid refluxAvoid alcohol and smoking; try antacids, H2 blockers, or proton pump inhibitors
BloatingAvoid gas-producing foods (eg, broccoli, beans, eggs); check for lactose intolerance; use antigas product
DiarrheaAvoid antibiotics, NSAIDs, caffeine, and high-carbohydrate sport drinks; reduce high-glycemic-index foods, especially before exercise
GI bleedingAvoid aspirin and other NSAIDs; stay hydrated

*Any person with GI bleeding or other symptoms that persist for more than 2 weeks should seek medical attention.

Many athletes get relief from over-the-counter (OTC) antacids. Using an antacid is all right as long as it is taken as prescribed; however, athletes should seek medical attention if their symptoms persist more than a couple of weeks. Antacids containing magnesium hydroxide, though, may act like old-fashioned milk of magnesia and produce diarrhea. On the other hand, antacids with aluminum hydroxide can lead to constipation.

I sometimes suggest a therapeutic challenge with H2 blockers like ranitidine. I recommend that athletes try 150 mg of ranitidine an hour before a competition. It works prophylactically for some. Now that H2 blockers are sold OTC, more and more athletes are treating themselves. Since the dose in the OTC formulation of ranitidine is only 75 mg, athletes need to take two tablets. If GI symptoms are recalcitrant to H2 blockers or proton pump inhibitors, a culture for Helicobacter pylori as well as additional GI workups—such as an upper endoscopy or upper GI series—should be considered.

For bloating, I look at dietary factors, like gas-forming foods (for example, broccoli, beans, and eggs) or lactose intolerance. Some patients gain relief with the OTC antigas products.

For patients who have lower GI symptoms, do you recommend antidiarrheal medications?

I don't, and that may make me somewhat different from other physicians. Antidiarrheal ingredients, such as loperamide, depress the central nervous system. In endurance athletes, I worry about their side effects, which include interfering with heat dissipation and with the ability to concentrate. As suggested earlier, it's important to rule out other causes of diarrhea, such as infectious agents, antibiotics, inflammatory bowel disease, or dietary factors. Once a thorough workup is completed on a patient, then a therapeutic trial of antidiarrheal medication may be considered, but the concerns for side effects with these medications should be discussed with the athlete.

Should people with inflammatory bowel disease continue to exercise?

There are currently no clear-cut answers to questions like this. Because of the lack of controlled studies, we often rely on case reports for answers. One case-control study (11) of 300 people with inflammatory bowel disease found that the relative risk of Crohn's disease was inversely related to physical activity. That's a good reason to stay active.

I tell my own patients who have inflammatory bowel disease—Crohn's disease or ulcerative colitis—not to exercise strenuously when their disease is active, especially when they're having bloody diarrhea. Does exercise in and of itself affect the disease? We're not sure. I'm concerned that intense exercise in patients who have such a condition might lead to gut ischemia that could worsen their bleeding.

Patients with inflammatory bowel disease and diarrhea need to be hemodynamically stable before they are allowed to exercise. Symptoms such as dizziness, fatigue, and shortness of breath can indicate hemodynamic instability and orthostatic changes. Tachycardia and low hematocrit and hemoglobin levels are important signs of hemodynamic instability. When their disease is stable, exercise can be performed safely, and evidence suggests it can help attenuate disease and improve mental well-being.

What other measures can help prevent exercise-related GI symptoms, assuming there is no underlying disease?

Modification and timing of exercise and food and fluid intake may decrease symptoms. In addition, as an individual becomes more fit, some symptoms may also lessen.

However, if GI symptoms persist, they should not be overlooked, because they could indicate more serious problems.


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Proper Hydration—Without Sloshing

The thirst mechanism is not activated until dehydration has already started, so it's important for active people, especially endurance athletes, to drink early in exercise. Doing so may offset exercise-related gut ischemia. However, some people can't stomach fluids during exercise, so how do these athletes stay hydrated?

The previous fluid recommendations set by the American College of Sports Medicine (ACSM) suggested that athletes drink 2 cups of water before exercise and 1 cup of water every 20 minutes during exercise. Running athletes have trouble competing with that much fluid jostling in their stomachs. Each person needs to find his or her optimal volume. It's not uncommon for elite runners to drink less than a cup of fluid during cool-weather runs that last more than 2 hours.

The newest ACSM guidelines (1) are more realistic. They still recommend the 2 cups of fluid before exercise, but, during exercise, they recommend consuming "the maximal tolerable amount" or drinking regularly enough to replace water lost through sweating. The new guidelines suggest that athletes "learn their tolerance limits for maintaining a high gastric fluid volume for various exercise intensities and durations." In addition, the use of electrolyte and carbohydrate solutions is helpful in exercise lasting longer than an hour and can help maintain electrolyte and glycogen stores.


  1. Convertino VA, Armstrong LE, Coyle EF, et al: ACSM Position Stand: Exercise and fluid replacement. Med Sci Sports Exerc 1996;28(1):i-vii

Athletes With GI Symptoms: Two Case Reports

Delayed Diagnosis in a Swimmer

A 19-year-old female collegiate swimmer sought medical care for bloody diarrhea that occurred while she was on summer vacation. During the previous swimming season, she had been diagnosed as having iron-deficiency anemia, as confirmed by serum iron studies. The condition was attributed to frequent, heavy menstrual bleeding, poor dietary intake of iron, and concomitant use of nonsteroidal anti-inflammatory drugs.

Further studies over the summer included upper and lower endoscopies, which confirmed ulcerative colitis. She was referred to a gastroenterologist, who treated her with aminosalicylates and prednisone, and her bleeding stopped. With iron replacement, her anemia resolved. She resumed training 3 months after initial presentation but was advised to curtail training if she actively bled and to seek attention whenever her symptoms recurred. A nutritionist advised her on proper diet. Her condition was controlled with aminosalicylates, and she was able to compete successfully.

Comment: If a more thorough evaluation had been done when the patient presented during the swim season, ulcerative colitis might have been uncovered then.

A Reticent Pitcher

A 20-year-old male collegiate baseball pitcher presented to his team physician with mouth ulcers that had been present for 1 week. He had had similar symptoms 6 months earlier, but they resolved on their own. When questioned directly, he admitted he currently had bloody diarrhea. He also reported having bloody diarrhea during the earlier episode but said he hadn't mentioned it because he didn't think it was important. (He had told his father, a physician, about the mouth ulcers but not about the diarrhea.)

The athlete was orthostatic and had minimal dizziness and fatigue with exertion. His hematocrit was on the low side of normal, but fell with rehydration. He was seen by a gastroenterologist, who performed upper and lower endoscopies with biopsy, which confirmed ulcerative colitis. He was treated with prednisone and aminosalicylates, and his bleeding stopped within 2 days. His hematocrit stabilized, and he was no longer orthostatic.

The gastroenterologist felt that exercise was contraindicated. The team physician suggested that the young man modify his exercise intensity and, given the position he played, allowed him to compete in the conference championship without adverse effects. He competed the following season, his senior year, without any problems.

Dr Putukian is a team physician at The Pennsylvania State University and an assistant professor of internal medicine, orthopedics, and rehabilitation at the Center for Sports Medicine, in University Park, Pennsylvania. She is a fellow of the American College of Sports Medicine. Ms Potera is a freelance writer in Great Falls, Montana. Address correspondence to Margot Putukian, MD, Pennsylvania State University, Center for Sports Medicine, 1850 East Park Ave, Suite 112, University Park, PA 16803.



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