runner and porta johns
Photo: BEN STANSALL / AFP via Getty Images

Reducing Runner’s Trots

Why running causes diarrhea and strategies to avoid mid-run pit stops.

runner and porta johns
Patrick Wilson

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Even though a hip injury prevents me from putting in much mileage these days, I can still vividly remember a winter morning in 2009 when my long, slow run of the week morphed into a speed workout consisting of sprinting back to my house to soothe an angry bowel. Thankfully, I was doing loops around my neighborhood and wasn’t far from home. I made it back just in time to scurry to the bathroom and reenact Harry Dunne’s infamous scene from Dumb and Dumber.

My experience is by no means an aberration, and it’s reasonable to assume that almost every seasoned distance runner has been seized by an irrepressible urge to void their bowels midrun. In the best-case scenario, a runner can find their way to a nearby lavatory, or at least a close bush, but in the worst circumstance, they may actually soil their britches.

While many people struggle to understand how athletes can soil themselves while exercising, a quick search of the internet reveals numerous tales of in-race bowel disas­ters, some of which involve top-level athletes. In truth, elite endurance athletes may be more predisposed to this sort of mishap simply because of their supernatural ability to push through discomfort. The loss of precious time from stopping to use the toilet may incentivize them to push the limits, poohaps too far. (Hey, if you can’t make poop witticisms in a book about gut distress, when can you?)

In other situations, athletes may stop to go number two but decide that making it to the Porta-John isn’t viable, either because it would take too much time or because there isn’t one nearby. Instead, they might opt to duck behind a shrub or a crowd barrier.

RADCLIFFE,PAULA-London Marathon 2002
photo: Mark Shearman

One of the most notorious of these cases comes from former women’s marathon world-record holder Paula Radcliffe, who, during the 2005 London Marathon, briefly stopped four miles before the finish to go number two in front of the world. Despite sounding like an unpleasant spectacle to watch, it’s hard to tell from video of the incident that Radcliffe actually had a poo, as she only briefly pulls over to the course barricade, quickly squats, yanks her shorts slightly aside, relieves herself, and thereafter hastily resumes running. Amazingly, despite her bowel troubles, Radcliffe went on to not only win the London Marathon but also set a world record for a women-only marathon. She later reportedly said, “I didn’t really want to resort to that in front of hundreds of thousands of people. But when I’m racing, I’m totally focused on winning the race and running as fast as possible. I thought, I just need to go and I’ll be fine.”

Running tends to bring on these symptoms the most; a study of marathoners from the Belfast City Marathon, for example, found that urges to take a dump were occasionally or frequently experienced by just over 40 percent of runners during difficult runs, which was roughly twice as high as during easy runs. What’s more, diarrhea occurs so often during and after running that a unique term exists for it: runner’s trots.


Anecdotally, pre-competition jitters are notorious for triggering urges to release the Kraken. Indeed, lines for Porta-Johns before big marathons can have wait times akin to that of the latest and greatest ride at Disney World. Beyond anecdotes, a study of over 60,000 Norwegians confirmed there’s a relationship between general anxiety and the occurrence of diarrhea. This research—along with the overwhelming volume of anecdotes I’ve heard—has led me to conduct my own research on anxiety and gut symptoms in endurance athletes.

runners waiting for porte-johns
photo: Patrick Ouellette/Portland Portland Press Herald via Getty Images

In one study, I recruited seasoned runners and asked them to journal about their running-related gut symp­toms over a month. Each runner rated six symptoms (including an urge to defecate) on a 0-to-10 scale after every run, and at the end of the month, they completed questionnaires on how stressed and anxious they had felt over the previous month. Long story short, ratings on the stress and anxiety questionnaires were positively correlated with the occurrence of gut distress (defined as 3 or higher on the scale). This meant that runners who reported more stress and anxiety were more likely to experience gut problems during their runs. It’s important to remember that the study was purely observational, meaning we can’t guarantee that anxiety and stress are solely to blame for the runners’ gut issues. However, if you consider these findings along with other sources of evidence, it’s hard to imagine how anxiety and stress wouldn’t play some sort of role in the defecation-related symptoms that many athletes experience in and around the time of competition.

A Matter of Timing

As with all gut symptoms, competition-day nutrition can play an outsized role in whether you stop midcompetition for the sake of saving your shorts. On the most basic level, eating provokes bowel urges because it initiates what’s called the gastrocolic reflex. Stretching of your stomach’s walls and the presence of digestive products in your small intestine cause signals to be sent, via your nervous system, to your colon, and these messages notify your colon that it needs to make room for an invading horde of partially digested foodstuffs. Your colon heeds this order by initiating giant migrating contractions, which are intense and sustained contractions that propel colonic contents forward.

A study published in the journal Gastroenterology, for instance, showed that colonic activity surged immediately after eating a 1,000-kilocalorie meal and peaked at nearly fivefold of baseline levels within about 30 minutes. To be clear, I’m not telling you to avoid eating before or during exercise; instead, this information should reassure you that having to poo is a natural response to eating.

Nutritional Choices

The nutritional choices you make during exercise can affect defecation-related symptoms for reasons other than the gastrocolic reflex. Although they can help fuel a winning performance, overconsuming carbohydrate-rich foods and drinks during exercise can also certainly provoke bowel urges. If they fail to be absorbed in your small intestine, carbohydrate molecules enter your large intestine, where they subsequently draw water from your blood into the luminal space, leading to loose stools or diarrhea.

As a parallel example, this phenomenon also occurs when a person ingests lactulose, a synthetic, nondigestible sugar that’s used as a laxative drug. Undigested lactulose travels through the small intestine and ends up in the large intestine, leading to a highly reproducible and dose-dependent increase in watery stool output. Similarly, anyone who is lactose intolerant is all too familiar with the diarrhea that ensues after downing sizable portions of dairy.

runners wait for porte-johns
Photo: Fabian Posselt/ullstein bild via Getty Images

Strategies for Avoiding Runner’s Trots

 Having the occasional urge to go numero dos while running is perhaps inevitable. However, there are several things you can do to reduce your chances of having to make a mad dash to the privy mid-run. If possible, avoid eating large meals within 30-60 minutes of important training sessions or competitions, especially in the morning, as it’s likely to provoke the gastrocolic reflux.

Also avoid overeating carbohydrate foods and beverages while exercising. Most people can comfortably handle 30–45 grams of carbohydrate per hour; if you decide to go higher, you should definitely practice that sort of fueling strategy at least 4 or 5 times in the weeks leading up to competition. Given fiber’s well-known stool-producing properties, you might also consider tapering your roughage intake starting 48 hours before racing.

Finally, if you’re the type of athlete the deals with nerve-induced loose stools, consider incorporating some relaxation techniques like slow deep breathing or mindfulness into your daily routine as well as during the pre-race period.

Excerpted and adapted from The Athlete’s Gut by Patrick Wilson, with permission from VeloPress.

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