The rundown on runner’s trots

Thanks to children’s book author Tarō Gomi, as toddlers we learned that everyone poops.

That’s certainly true for runners, even (and especially) when we’d rather not — like midway through a long run, or two miles into a big race.

There is no showstopper quite like having to go on the run.

Running certainly seems to exasperate gastrointestinal (GI) issues, and “runner’s trots” is a phrase for a reason.

In fact, anywhere between 20–80 percent of runners experience some sort of GI distress (nausea, gas, cramping or diarrhea) during or immediately following running, says Lisa Lovejoy, MEd, RD, CSSD, CD, a sports dietitian for MultiCare Orthopedics & Sports Medicine.

Lovejoy explains that while the cause isn’t really known, the issue could be attributed to a few factors:

Jostling nature of running. Your insides slosh around a bit with the repeated impact of running, making GI issues much more common in runners than in swimmers or cyclists.

Fast pass. Exercise increases the rate at which food moves through the GI tract, reducing the time between consumption and elimination. The plus side of this faster digestion may be that runners tend to have a lower incidence of cancer.

Body function prioritization. During exercise, blood flow is directed toward working muscles, and thus away from the GI tract, which can lead to intestinal problems.

Bad timing. Poorly timed eating or drinking habits, such as eating heavily or drinking too much coffee before a run, are known GI irritants.

Race day jitters. Nerves and the associated hormonal responses affect the GI system. Your adrenaline is pumping, and if your body is reading this as a fight-or-flight moment, your body wants to pare down to the essentials.

Fueling on the run. Consuming nutritional running fuel, especially goos, gels and bars, can cause GI discomfort. Their high sugar concentration (by design) can draw water into the gut and lead to an upset stomach. You can reduce this effect by drinking plenty of water alongside these items to help dilute the sugar load.

Dehydration. Lack of fluids can exacerbate stomach issues. It’s important to hydrate well before a run and ensure those fluids contain electrolytes.

Unrelated conditions. Some people may have undiagnosed conditions, such as lactose intolerance or irritable bowel disease (IBD) that contribute to GI distress.

Some causes can’t be avoided, such as a jostling stomach, but Lovejoy explains some ways to prevent an episode:

Respect the two-hour window. The general rule is no solids two hours before a run, but find a strategy that works for you. Keep it simple and avoid foods that are loaded with sugar or hard to digest.

Keep it calm. Reduce or eliminate the consumption of stimulants the day before a race. These include caffeine (responses vary individually, so experiment with this); spicy, gassy, high-fat foods; and, for susceptible individuals, dairy foods. Artificial sweeteners, especially sugar alcohols (sorbitol, mannitol, xylitol) and fiber additives (inulin or chicory root, common in many energy bars) may contribute to diarrhea at any time, especially with the added stress of exercise.

Pass on fiber. While fiber is usually considered to be part of a healthy diet, reducing it the day before an event may lessen GI distress.

Gel well. If you do use running gels or goos, be sure to drink plenty of plain water along with them and consume these items while you train. Don’t try anything new on race day!

Build slow. Gradually increasing training distance or intensity should also help give your gut time to adapt to your new habits.

Some of the above suggestions are sweeping best practices, but of course there are individual exceptions. Practice makes perfect. For example, practice eating the same breakfast before every long run.

Lovejoy is “a big fan of using food records to identify trends” and suggests including your fuel notes alongside your training journal, including what you ate as well as when and how it made you feel. You’ll start to identify patterns for yourself.

Of course, sometimes you’ll do everything right and still end up cramping mid-run and looking for the nearest bathroom (or tree). The best way to make it to the next pit stop in an emergency is to walk — it can really calm your stomach down.

And if you find that it’s constantly happening around the same mile point, plan your loop accordingly. Luckily, Lovejoy says, “most runners feel significantly better after voiding and can return to their run.”

GI issues on the run happen to everyone at some point. If you bring it up with a group of runners, everyone has a horrifying (and hilarious) story to tell.

In the moment, it’s awful, but there’s no shame. Welcome to the runners’ club!

This article was originally published June 2017 and updated June 2023.