Runner’s diarrhea, also called “runner’s colitis” and “runner’s trots,” refers to a condition that affects runners during and after a run. Long-distance runners (those who run 3 miles or more at a given time) are the most likely to experience this. When you have runner’s diarrhea, you experience frequent bowel movements during and right after your run. In one study of long-distance runners, 62 percent of those participating reported having to stop during a run to have a bowel movement.

While doctors aren’t completely clear on what causes this to happen, there are ways to identify and manage runner’s diarrhea.

Actual diarrhea is only one of the symptoms of runner’s diarrhea. Other symptoms you may experience include:

  • gas
  • acid reflux
  • nausea
  • cramping

The symptoms of runner’s diarrhea will typically begin during your workout and may continue in the hours after you’re done running. Runner’s diarrhea shouldn’t last for more than 24 hours. If you get diarrhea during a run and your loose bowel movements don’t stop, it may be a sign of another medical condition.

Diet and lifestyle changes

There are steps that you can take to decrease your chances of experiencing runner’s diarrhea. Most of the treatment relates to your diet, particularly what you choose to eat in the hours and days prior to a long run. You may also consider what you wear while you’re running, as clothing that’s too tight around the midsection can constrict blood flow to your digestive tract and make your symptoms more uncomfortable.

Over-the-counter treatments

Over-the-counter treatments, such as bismuth salicylate (Pepto Bismol) and loperamide (Imodium) might be an option to stall the diarrhea after your run, but be careful. Taking these medications on an empty stomach might just make you feel ill.

Treating underlying conditions

You might also want to try to determine if you have a lactose intolerance, or if you have an underlying condition such as irritable bowel syndrome (IBS). One study showed that people with these conditions were much more likely to experience runner’s diarrhea. For those people, switching up their diet was the biggest part of the solution to their symptoms.

The simplest way to treat runner’s diarrhea is to address your pre-run eating habits. Certain foods can trigger diarrhea and make gas and nausea during a run more likely to occur. Start by thinking of what you tend to eat immediately before a run, and work backward as you eliminate foods.

In the two hours before your run is set to begin, try to avoid eating anything besides a quick energy-boosting snack, like whole-wheat toast or a banana. Avoid caffeine of any kind in the time period immediately before you run, as it works as a diuretic. If you tend to have runner’s diarrhea, try cutting back on artificial sweeteners, sugars, and alcohol on the evening prior to your run.

Beware of energy gel packs and supplements that are supposed to provide easy, portable “fuel” during a run. Many contain artificial sweeteners and preservatives that can trigger diarrhea. Above all, always stay hydrated before, during, and after your run. Staying hydrated can make all the difference in your athletic performance.

As with any form of diarrhea, you should watch for dehydration if you have runner’s diarrhea.

Emergency symptoms include:

  • severe heart palpitations
  • acute headache that comes on suddenly
  • fainting or loss of consciousness
  • bloody or black stool
  • diarrhea that lasts for 24 hours or more

By experimenting with what you eat and what time of day you run, you may be able to stop runner’s diarrhea from happening during your runs. Always be wary of dehydration. The sweat you lose during a long run, in addition to diarrhea, can compound your risk of losing too much fluid. If you have tried to change your diet and your running habits and you’re still experiencing runner’s diarrhea, you may need to speak to a nutritionist or a sports medicine specialist.