Runner's Diarrhea: Causes and Prevention

Runner’s diarrhea, runner’s trots, the indian shimmy, runner’s colitis, or just stinky pain in the butt – whatever you choose to call it makes no difference.

It’s uncomfortable, sometimes painful, and always embarrassing.

And it affects your running performance negatively.

Perhaps unsurprisingly, there’s literally nothing to like about having to empty your bowels while running. This is true whether you’re running by yourself on a treadmill or trying to outrun your opponents in a race.

So let’s talk about this all-too-common problem and the steps that you can take to mitigate or even solve it.


What is Runner’s Diarrhea?

It’s human nature to face an issue and reflexively think, “why me?”

But gastrointestinal problems in runners are way more common than you think.

Studies show that up to 60% of long-distance runners have the urgent need to defecate while running.

The truth is that despite all of its scientifically-backed benefits, running also comes with its own problems. In fact, running is a known cause of a variety of digestive issues like acid reflux, heartburn, and even frequent bowel movements on and off the pavement. That’s why you may have noticed that your trips to the bathroom have become much more frequent ever since you took up running – it’s totally normal and even to be expected.

Again, it’s estimated that more than half of runners experience what you do.

The thing is though that your frequent and relatively benign trips to the bathroom can become a serious issue if you’re not careful. While some bloating and tummy aches and flatulence and defecation are nothing to worry about, if you discover blood in your stool, you should worry. That’s why it’s imperative that you learn to recognize the symptoms of runner’s diarrhea and learn to differentiate them from more severe conditions that require medical attention.

Recognizing the Symptoms

The first thing you should know about runner’s diarrhea is that it doesn’t last that long. In fact, if you ever stop running (though we hope you never do!), you may find that the problem disappears almost immediately.

As a general rule of thumb, you should only feel discomfort during your run and maybe (though not always) a few hours after it. If the discomfort lasts for over 24 hours, it may be indicative of a more serious underlying issue. This is especially true if you continue to experience diarrhea after that time frame.


The exact cause isn’t actually known. What we have instead is a couple of sound theories.


The heart is constantly pumping blood – and with that blood, oxygen and nutrients – to the various parts of the body that need it most in the moment. So the amount of blood a part of your body receives is dependant on what you’re doing right then and there. Ischemia, simply put, occurs when a part of your body isn’t receiving enough oxygen.

When what you’re doing is running, your glutes require more blood and oxygen and nutrients than any other body part – including the stomach. Studies show, in fact, that blood flow to the stomach and to other internal organs can actually decrease by up to 80%! This lack of oxygen makes the mucus lining of the intestines vulnerable and more susceptible to penetration.

Remember, this mucus lining is there to protect your intestines. Although there’s no definitive science to back this theory up, digestive disturbances could be caused by some minor damage to intestinal tissue. The effects of this could theoretically last for a day or so until the body repairs itself.


As with side cramps, calf cramps, fatigue, headaches, and so much more, one of the possible causes of diarrhea is dehydration.

If the other side effects of dehydration don’t compel you to be very meticulous about proper hydration, perhaps this embarrassing one will.

Ironically, diarrhea is the most common cause of dehydration; but dehydration itself can cause diarrhea too, which can make you even more dehydrated. Again, proper hydration is absolutely essential.

Running Itself

Unfortunately, running itself is thought to cause runner’s diarrhea just by its very nature.

It makes sense.

But if ischemia were indeed the main culprit, athletes from different sports like cycling or swimming would experience digestive issues at the same rate as runners.

This just isn’t the case. And even among runners, studies show that the more one runs, the likelier it is that they’ll have digestive issues. In fact, professional runners are up to three times as likely to experience diarrhea than your average recreational runners.

In other words, more running equals more diarrhea.

The direct cause for this seems to be the jostling of the internal organs when you run. When you bounce up and down and hit the ground with force (even if you’re running properly), your internal organs are bouncing around too, which may be leading to digestive troubles.

For some more information on what can cause diarrhea in runners, check out the video below.

Treatment and Prevention

Unfortunately, there’s no way to keep your organs from jostling as you run. So if that’s indeed what’s causing your problems, then there’s really not much anyone can do about it – like we said before, lots of runners deal with the issue. It’s best to think of it as part of the sacrifice.

What you can do, however, is watch what you eat and when you eat. It’s particularly important in this case to watch what and when you eat before you run. The thing to remember if you’re struggling with this particular issue is to refrain from eating for at least 2 hours before you run. Give your body enough time to digest what you’ve eaten and to convert it into useable energy.

Remember that adage that compels you to change what you can and let go of things that you can’t?

Heed it.

Pay attention to your diet and remember to always, always, always hydrate properly.

Foods to Avoid

Unsurprisingly, there are foods that are more likely to make your problem worse. These should be avoided, particularly during training or before a big race.

Here are the general guidelines you should follow:

  • Refrain from eating any high-fiber, gas-inducing foods three-to-four hours before your runs or 24 hours before a big race. These include salads, fruits, lentils, beans, and legumes. Certain cereals should be avoided too.
  • Avoid spicy foods at least a day before running.
  • Three-to-four hours before running, avoid caffeine. That means most energy drinks and coffee.
  • Avoid artificial sweeteners. These, if taken in excess, can actually be used as a laxative. As we’ve seen, running is already enough of a laxative – don’t exacerbate the issue.
  • Avoid alcohol

Final Thoughts

While the problem may never go away completely for as long as you keep running, the steps taken above should help significantly.

If your symptoms persist, we recommend you get checked out by a medical professional who can determine if you have an underlying condition like irritable bowel syndrome or lactose intolerance.

If in addition to loose bowel movements you also experience accompanying headaches or dizziness, heart palpitations, fainting, black or bloody stool, or if your symptoms last for more than 24 hours, make sure to consult with a doctor.


Have any questions? Concerns? Make sure to leave them in the comments below.


  1. PopSci
  2. Active
  3. MayoClinic
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