---
title: "Runner's Trots: How to Prevent Diarrhea on a Run"
description: "Runner's trots disrupting your runs? Learn what to try with food, fuel and timing, what to do mid-run, and when diarrhea needs medical attention."
url: "https://wisdomrunning.com/runners-trots/"
language: "en"
author: ["Alex Gorovenko"]
published: "2026-10-20T15:57:38.000-07:00"
modified: "2026-10-20T16:05:01.000-07:00"
tags: ["Training","Running Tips"]
---

# Runner's Trots: How to Prevent Diarrhea on a Run

![Runner holding a water flask beside a park restroom before setting out on a path](https://wisdomrunning.com/content/images/2026/10/runners-trots-park-restroom-route-v2.webp)

Runner's trots is the common name for a gut problem tied to running. The symptoms are loose stools or a sudden need for a bathroom. They can hit during a run or soon after you finish. Look at the fuel you use in training, meal timing and possible food triggers to reduce repeat episodes. Begin with one change that you're able to track. Cutting out whole food groups isn't the place to start.

Blood in the stool, severe pain or signs of dehydration call for medical attention, even when symptoms start on a run.

## What to do if diarrhea starts during a run

Ease back to a walk and look for a bathroom. If you keep having loose stools, feel weak or dizzy, or have significant pain, end the run. Ask a volunteer at a race to direct you to the medical team. The rest of the distance can wait.

Once you're somewhere comfortable, replace lost fluids and electrolytes. Water with food or broth may help; an oral rehydration solution is another option. If you have kidney disease, diabetes or another condition affecting fluid intake, ask your clinician what to use. The [NIDDK's diarrhea treatment guidance](https://www.niddk.nih.gov/health-information/digestive-diseases/diarrhea/treatment) also advises returning to your usual diet as your appetite comes back.

Hold off on your next run until the diarrhea has settled and you feel well enough to exercise. Because causes of diarrhea differ, no single restart time fits all of them.

## When to get medical help

**Blood in your stool is not something to write off as runner's trots.** Get medical advice promptly for blood or black, tarry stools, severe abdominal or rectal pain, frequent vomiting, or signs of dehydration such as dizziness and much less urine than usual.

For adults, [NIDDK also advises contacting a doctor right away](https://www.niddk.nih.gov/health-information/digestive-diseases/diarrhea/symptoms-causes) for a high fever, six or more loose stools in a day, or diarrhea lasting more than two days. Don't wait for that time limit if another warning sign appears.

If episodes keep disrupting your training, book an appointment. The same goes for symptoms that happen when you aren't running. A clinician can look for other causes, including an infection, a food intolerance or a medication effect. Bring a record of when symptoms happen, even if they seem connected to exercise.

## Why running can upset your gut

Several things may contribute to gut trouble on a run: less blood reaching the intestines during exercise, repeated jostling and pre-race nerves. Food, fluids and how hard or long you run also matter. [Mayo Clinic describes several possible contributors](https://sportsmedicine.mayoclinic.org/news/how-can-i-prevent-runners-diarrhea/), rather than one established cause.

The timing alone doesn't tell you what's causing the symptoms. You might have an urgent bathroom trip while the stool itself stays normal. Repeated watery diarrhea isn't the same thing, though. Make a note of which you have. That way you can describe it when you speak with a healthcare professional.

## How to prevent runner's trots

First, look at what's changed in your routine. Maybe you had a new breakfast. A different gel or a harder session could also be the change. That's a practical place to begin. It also saves you from drawing up a long list of foods to avoid.

Choose a familiar, easy route near an open restroom once symptoms have settled and you feel ready to run again. Keep a brief note of what and when you ate, drinks, fuel, weather, effort and any symptoms. Try changing one possible trigger at a time. This lets you see whether the adjustment makes a difference. Your notes can help you spot patterns to discuss with a clinician. They can't diagnose the cause.

The [American Medical Society for Sports Medicine](https://www.sportsmedtoday.com/runners-trots-va-171.htm) includes meal timing and individual food triggers in its guidance. Choose an adjustment that fits the pattern you've noticed:

| What you notice | A change to try |
| --- | --- |
| Urgency follows pre-run coffee | Try less coffee or have it after the run; note caffeine in gels too. |
| A large, fatty or high-fiber meal upsets your stomach | Move the larger meal earlier and choose a smaller, familiar pre-run option. Keep nutritious high-fiber foods elsewhere in your day. |
| Sugar-free gum or sweets are part of your routine | Check for sorbitol or other sugar alcohols and try leaving that product out. |
| Dairy causes symptoms and you know you have lactose intolerance | Use a tolerated lactose-free alternative rather than removing every dairy food. |
| Problems started with a new gel, drink or serving size | Return to the last tolerated routine, then test the product and amount separately in training. |

The sugar-free label deserves a second look if you like [chewing gum while running](https://wisdomrunning.com/chewing-gum-while-running/). It says nothing about whether your gut will tolerate the sweetener.

Say you changed breakfast on the same weekend that you added a caffeinated gel. Repeat both and you still won't know which might be causing trouble. Return to the breakfast and fuel routine you previously tolerated. Do this on a suitable training run. Write down how that run went before you change anything else. Take those notes to a clinician rather than cutting out more foods if symptoms persist.

### Keep fueling, but rehearse it

While you work on digestive comfort, keep enough fuel for your session. You can adjust portion size and timing or change the kind of carbohydrate. You don't have to skip food altogether to do that.

[Monash University's sports-fueling guidance for people with IBS](https://www.monashfodmap.com/blog/low-fodmap-sports-fuelling-guide/) gives a meal three to four hours before exercise and a small, low-fiber, low-fat snack 30–60 minutes beforehand as possible options. Those are starting points to individualize, not rules that every runner must follow. A small piece of familiar toast may suit one runner; another may need more time after eating.

On longer runs, practice the fuel you plan to carry, including its amount and timing. A review of [gut training in athletes](https://pubmed.ncbi.nlm.nih.gov/28332114/) describes how digestive comfort may adapt to repeated practice, while noting limits in the human research. It doesn't promise that a particular gel will stop diarrhea.

Keep race day familiar. Work on [your fueling plan](https://wisdomrunning.com/hitting-the-wall-how-to-avoid-marathon-wall/) during training if you're preparing for a marathon. Do that rather than reacting to one bad run by dropping all fuel.

### Plan fluids and an easier route

Make fluids accessible before, during and after the run, but don't force large amounts in an attempt to prevent diarrhea. The [National Athletic Trainers' Association](https://www.nata.org/press-release/nata-publishes-new-fluid-replacement-physically-active-position-statement-journal-athletic-training) warns about both dehydration and overdrinking. Your needs depend on conditions, sweat losses and the session.

If symptoms return, a short loop near home or a park restroom makes it easier to stop. Make sure that restroom is open at the time you plan to run. Locate toilets and medical stations before the start of a race. Leave enough time for a bathroom visit that doesn't feel rushed.

Does trouble mainly appear on hard or long efforts? Then cut back the intensity or distance while you figure out what's happening. You can also choose a cooler time of day. Changes like these make the next session easier to manage. They aren't a substitute for an assessment of recurring diarrhea, though.

## Be careful with medication and restrictive diets

Don't take nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen or naproxen, just to get through a run. In a [small study of nine trained men](https://pubmed.ncbi.nlm.nih.gov/22776871/), ibuprofen worsened markers of small-intestinal injury during cycling. That study wasn't a diarrhea trial in runners, but it supports caution about taking these drugs around exercise. If a medicine is prescribed, discuss changes with the prescriber.

You'll find loperamide sold under the brand name Imodium. Taking it shouldn't become an automatic pre-race habit. The American Medical Society for Sports Medicine describes the results with antidiarrheal medication as mixed. The group recommends an individual discussion with a sports medicine physician. Some diarrhea shouldn't be self-treated with an over-the-counter antidiarrheal. That includes bloody diarrhea and diarrhea with fever. Seek medical advice for those.

A low-FODMAP diet is also more involved than avoiding a few foods before a run. It changes intake of certain fermentable carbohydrates and is used for medically diagnosed IBS. [Monash recommends dietitian guidance and reintroduction of tolerated foods](https://www.monashfodmap.com/ibs-central/i-have-ibs/starting-the-low-fodmap-diet/), rather than permanent broad restrictions.

If basic adjustments haven't helped, take your run-and-food notes to a healthcare professional. A sports dietitian can help you work on tolerance while you keep enough food and variety in your diet to support training.

## Frequently asked questions

### What are runner's trots?

Runner's trots is a common nickname among runners. It refers to diarrhea or an urgent need for a bathroom. Both can strike during or just after running. The name describes the symptoms but doesn't tell you what's causing them.

### How long does runner's diarrhea last?

That depends on what's causing it. Contact a doctor if diarrhea lasts more than two days, and seek help sooner for blood, severe pain, dehydration, high fever or frequent vomiting.

### Can coffee cause runner's trots?

It can for some runners, since caffeine is a possible trigger. If symptoms follow your pre-run coffee, try changing the amount or timing. Keep in mind that some gels contain caffeine as well. You might not have to give up coffee entirely.

### Should I run on an empty stomach to prevent diarrhea?

Not necessarily. Try adjusting meal size, food choice and the time between eating and running. Keep enough fuel for your session while you do. Avoid turning a stomach problem into a routine of underfueling long runs.

### Should I take Imodium before a race?

Discuss recurring symptoms and medication with a clinician instead of taking it automatically. Antidiarrheals aren't the right choice in every situation. They're especially not for diarrhea with blood or fever. That needs medical advice.

### Can I prevent runner's trots every time?

No strategy guarantees it. A familiar fueling routine, sensible fluid intake and a record of your triggers can help you make informed adjustments. Get repeated episodes assessed. Don't keep restricting more and more foods.