Why Running Makes You Poop, According to a GI Doctor

If you’ve ever been midway through a run and experienced that urgent, need-a-bathroom-right-now feeling in the pit of your stomach, you’re not alone. Over 800 people a month search the question, “why does running make you poop?” looking for answers. So we talked to Linda Nguyen, MD, a gastroenterologist at Stanford Health Care, to find out.

It turns out that this dire need to go “number two” on a run, is also known as runner’s trots and it happens to many runners. In fact, research out of Old Dominion University showed that runners typically experience at least one GI symptom on the majority of their runs (78–84%). While you can bank on the tried-and-true tradition of plotting running routes with bathroom stops, sometimes it’s not deal to stop mid-run to hit up a public bathroom. Other times, there’s just not one around when you need it. That’s why we asked Dr. Nguyen break down runner’s trots and more importantly, is there any way to prevent it?

Experts Featured in This Article:

Linda Nguyen, MD, is a gastroenterologist at Stanford Health Care.

Why Does Running Make You Poop?

Runner’s trots happens because strenuous exercise (like running) triggers a response from your sympathetic nervous system, Dr. Nguyen tells PS. Your SNS is a part of your autonomic nervous system, which controls bodily functions that you don’t have control over, like the beating of your heart, sweating, and digestion. The sympathetic nervous system is also controls your “fight or flight” response, and revs your body up “when you’re under stress,” Dr. Nguyen explains, like during intense exercise such as running. That response can also affect your digestion, increasing motility (the contraction of muscles within your gastrointestinal tract), leading to diarrhea.

The more strenuous the run, the worse your symptoms can be. “Marathon running is associated with more GI issues than a slow, casual jog,” Dr. Nguyen says. Studies have actually shown that extremely long runs such as marathons force your body to redirect blood from the gastrointestinal (GI) tract and send it to your muscles. That can be an issue, because “you need blood flow to the gut to digest and break down food,” Dr. Nguyen tells PS. Without it, your digestion can be affected, causing GI distress.

How to Prevent Runner’s Trots

Every body is different, but there are a few common tricks and tips Dr. Nguyen suggests for avoiding runner’s trots. For starters, be mindful of when you eat, she says. Not eating before a run can help you avoid the urge to poop. If you’re running for longer than an hour, though, you’ll probably need a snack beforehand to keep your energy up. When that’s the case, Dr. Nguyen says to avoid the following foods, all of which can trigger a more immediate GI response:

Basically, you want to avoid eating FODMAP foods. FODMAP is an acronym that stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, all ingredients that Dr. Nguyen says can cause GI distress before a run, especially if you struggle with irritable bowel syndrome.

Instead, Dr. Nguyen suggests the following:

It’ll require some trial and error to see what pre-run snacks are best for you; some people actually find that a small piece of fruit with some peanut butter or a NutriGrain bar works well, though if you have issues with IBS or eating FODMAPs, they might not be the choices for you. Try a few different options (here are more preworkout snacks to try) and see what you like the most.

If you’re dealing with the urge to go number two on a run, Dr. Nguyen says there’s really not much you can do but head for the nearest bathroom. If it’s happening on a regular basis, try changing your pre-run snack or going without food, if the run isn’t too long. Stress can also cause GI issues on a run, Dr. Nguyen adds; think of the flood of stomach-churning nerves you get before a race. If that’s the case, she recommends meditation and deep breathing, which can calm your gut and relieve cramps. Peppermint tea or peppermint oil can also be helpful.

Maggie Ryan was an assistant editor at PS. A longtime runner and athlete, Maggie has nearly four years of experience covering topics in the wellness space, specializing in fitness, sports, nutrition, and mental health.