By Danny Mackey M.S., C.Ped

I am sure every runner knows the scenario...the curious washing machine sound in your stomach during the first two miles, then all of a sudden you have to tell your teammates to “wait a sec” as you jump into the fortuitously placed Port-a-John on a construction site… now the washing machine sounds turn into monster type gurgle...and your teammates are annoyed as you end up in some neighborhood bushes. Fun times. 

You probably know the basics like; “Milk was a bad choice” or not eating a pulled pork sandwich while you are lacing up your running shoes (my buddy seriously did this last week). But what do the experts say?

Lucky for us there are brilliant people like Dr. Barry Schlansky that happen to think running and the G.I. systems are cool. Dr. Schlansky is currently a clinical fellow in gastroenterology and hepatology at Oregon Health & Science University in Portland. He completed medical school at Jefferson Medical College in Philadelphia in 2006 and an internal medicine residency at the University of Washington in Seattle in 2009. Dr. Schlansky has a soft spot for track and field from his fond memories of running cross-country while in high school in central Pennsylvania.

DM : It is normal for people to have some GI stress symptoms from time to time, but why is it that distance runners seem to experience these symptoms with more frequency?

BS : Well, intense exercise such as running requires that the body make a number of changes very quickly to ensure adequate delivery of oxygen to the muscles in the extremities (extremities in a runner's situation would be the working skeletal muscles, or in other words your legs). Oxygen delivery to these working/active skeletal muscles can increase 15 times during strenuous activity compared to a resting state. We have a finite amount of blood in our body. So your body accomplishes this feat by diverting oxygen-rich blood away from the skin and abdominal organs, down to your legs instead. It is no coincidence that many abdominal symptoms that are related to exercise stem from the decrease in blood flow to abdominal organs. The blood flow may be reduced by as much as 50-80% during prolonged high-intensity exercise.

DM : So if someone is doing a tempo run of 40 minutes or even something long and intense like multiple mile repeats, can it have an effect even after the workout is concluded?

BS : Right, the longer or more intense the workout is, it will increase the symptoms during and after the workout.  The intensity of sustained exercise required to divert enough oxygen away from the abdominal organs to cause symptoms is fairly high, and usually occurs only in hard efforts with fit individuals for that reason.

DM : If you read up on the GI stress, the words “reperfusion” and “oxidative stress” show up, can you define those a little bit more for us?

BS : Sure. You have to take a step back and know the initial problem for the body.  The harm to tissues caused by inadequate oxygen supply (from poor blood flow) is termed ‘ischemia,’ and this is the same mechanism that causes injury to the heart or brain tissue during a heart attack or stroke, respectively. Reperfusion and oxidative stress are the second problem, which occurs after exercise is concluded. At that time, the skeletal muscle no longer needs large amounts of oxygen, and your body diverts blood back to the abdominal organs; this is termed “reperfusion.” The influx of oxygen to the vulnerable ischemic tissues can result in a chemical reaction called “oxidation,” which is thought to be the basis for additional injury to tissues after exercise has stopped.

DM : Maybe it seems like everyone I know has some sort of stomach problem, but how common are GI symptoms in runners?

BS : Studies show that the majority of endurance athletes experience gastrointestinal symptoms – greater than 80% of elite marathon runners.  Symptoms are more common in women, younger athletes, those who ate within 2-3 hours of the exercise, and athletes who experience marked dehydration.  Lower gastrointestinal symptoms (abdominal pain, diarrhea, and rectal bleeding) are more common than upper gastrointestinal symptoms (heartburn, nausea/vomiting, and belching).  I wish I could tell you “why,” but to be honest, at this point the associations are unknown.

DM : Why do you see this more in female athletes?

BS : Same answer here, I wish I could tell you why, but this is also unknown. But, some female endurance athletes have reported gastrointestinal symptoms occurring more frequently with exercise during their menses, which implies that there may be female-specific hormonal differences related to their symptoms.

DM : I have a lot of runner friends that also ride for cross training.  They rarely experience GI problems on a bike.  I’m sure it has to do with pounding (also from personal experience of running long downhills) but is there a “why” to this experience beyond saying “the pounding from running causes you to poop your pants?”

BS : (Laughing) Running is thought to be particularly stressful on the abdominal organs because it is both a high-intensity and high-impact exercise.  Not only is blood flow to these organs greatly reduced, but also the pounding you mention shakes things up quite a bit.  Just as your bones and muscles are held together with ligaments and tendons, there are ligaments in your abdomen that connect the organs to the diaphragm.  There is increased strain on these ligaments during running compared to cycling or swimming.  Additionally, researchers have hypothesized that friction between the organs and the lining of the abdominal wall with pounding exercise may cause irritation that causes symptoms.

DM : What can we do to prevent these symptoms from occurring?

BS : It depends which symptoms predominate.  Exercise-induced diarrhea or vomiting is often reduced with avoidance of high sugar, high calorie, and high fat foods for several hours before exercise, and ensuring adequate hydration.  For heartburn, drugs that reduce stomach acid production have been shown to reduce the amount of stomach acid during exercise, but the studies do show heartburn symptoms didn’t improve. Like diarrhea, avoidance of meals for several hours before exercise is also crucial for this group, but heartburn-causing foods specifically should also be avoided, such as spicy food, coffee or tea (both caffeinated and decaf), citrus, dairy, and alcohol. With diarrhea, any bloody bowel movements should always be evaluated by a physician. 

DM : Are there any concerns between bloody bowel movements and being anemic?

BS : Yes, because it is also possible to lose small amounts of blood in the gastrointestinal tract that is invisible to the naked eye but can result in iron deficiency. Iron deficiency clearly impacts exercise performance, and studies have shown that it can be prevented with drugs that suppress stomach acid (this should also be managed by a physician).

DM : Speaking of being anemic, I’ve had a few athletes tell me their MD diagnosed them as being anemic but after further pushing and analysis we discovered they have been experiencing “dilutional pseudoanemia.” What should athletes know about dilutional pseudoanemia?

BS : Blood is composed of many things, but in terms of exercise, the most important constituent are the red blood cells, which carry oxygen to tissues bound to a protein, hemoglobin. When the volume of red blood cells relative to the rest of blood (called plasma) is low, this is termed anemia. Dilutional pseudoanemia, or “sports anemia”, is a false anemia that occurs after endurance exercise. What occurs is that during exercise the athlete loses body fluids from sweating and from the passage of water from the blood vessels to the muscles; thus, the volume of red blood cells relative to plasma actually increases during prolonged exercise due to this dehydration. After endurance exercise, the plasma volume expands, and can “overshoot” the original level before exercise, making it appear as if an anemia is present. This is not harmful to the athlete as it is not a true anemia, and no treatment is required. However, it is considered a diagnosis of exclusion, so other true causes of anemia, such as iron deficiency, need to be ruled out first by a physician before the dilutional pseudoanemia diagnosis can be made.