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Exercise make you need a poo? A gut expert explains what’s going on

Exercise make you need a poo? A gut expert explains what’s going on

If your stomach has a habit of joining your workout uninvited, a gut dietitian explains why, and what you can do about it.

Liubomyr Vorona/Getty Images

Ruairidh Pritchard

Published: September 17, 2026 at 10:18 AM

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You’ve found 45 precious minutes between work, school runs and everything else. Your trainers are on, you’ve actually made it out of the house, and then your stomach decides it has other plans. Suddenly, the only PB you’re interested in is how quickly you can find the nearest loo.

It’s an uncomfortable side of exercise that doesn’t tend to make the motivational Instagram posts, but sudden bowel problems during a tough workout are very real. And if you’ve seen that viral footage from HYROX Beijing, you’ll know they can happen to even the fittest athletes.

Australian athlete Joanna Wietrzyk suffered a bowel accident mid-race, but carried on competing and went on to win. Footage of the incident quickly spread across social media, sparking a debate about hygiene and why officials allowed her to continue using shared equipment.

HYROX later apologised, with co-founder Moritz Fürste admitting the organisation had made a mistake by “not reacting immediately during the race”, and announced new rules and procedures.

But the incident also raised a question that will be familiar to anyone with IBS or a temperamental gut: why can exercise suddenly make you need the loo?

Why can exercise suddenly make you need the loo?

First things first, what happened to Wietrzyk doesn't mean she has IBS, and there has been no suggestion that she does.

But according to Kirsten Jackson, Consultant Dietitian and founder of The IBS Dietitian, gastrointestinal problems during strenuous exercise are more common than you might imagine.

What happened at HYROX may sound extreme, but gastrointestinal symptoms during intense endurance exercise are surprisingly common.

Kirsten Jackson, Consultant Dietitian and founder of The IBS Dietitian

"When you're exercising hard, blood flow is diverted away from the gut towards the working muscles", explains Jackson, "Combine that with the physical impact of running, dehydration and race-day nerves, and you can experience cramping, nausea, diarrhoea and very sudden bowel urgency.”

In other words, your digestive system isn't necessarily being dramatic for the sake of it. Your body is busy sending resources elsewhere, while running adds physical movement and dehydration, and nerves can pile on further pressure.

What can you do if you have IBS or a sensitive stomach?

You don't need to be chasing a HYROX time to experience exercise-related gut problems. A hard Parkrun, gym class or long Sunday run can be enough to discover that your digestive system has other plans.

Jackson recommends thinking about what goes into your body before exercise, rather than simply avoiding food altogether.

1. Don't just skip eating

Going into a workout on empty might seem like the obvious solution, but Jackson warns against simply eating less.

“You also have to balance this against fuelling properly. Carbohydrate is incredibly important because we want to maximise glycogen stores before an event rather than under-fuelling in an attempt to keep the gut completely empty.”

Instead, she suggests choosing carbohydrate sources you already know you tolerate.

2. Know your personal trigger foods

For athletes particularly prone to diarrhoea or urgency, Jackson sometimes uses a temporary reduction in high-FODMAP foods for around 48 hours before a race.

FODMAPs are carbohydrates that aren't always fully absorbed in the small intestine. In susceptible people, they can contribute to bloating, gas, loose stools and urgency.

Crucially, Jackson isn't suggesting everyone needs to adopt a restrictive low-FODMAP diet. She describes this as a short-term strategy for someone who already knows their gut is sensitive.

3. Check your gels and sports drinks

That expensive running gel promising to propel you towards a PB isn't automatically your stomach's best friend.

Jackson says some gels, energy sachets, electrolyte powders and drinks can contain high-FODMAP ingredients, large quantities of certain sugars or sugar alcohols.

“Just because something is marketed for sport doesn't mean your gut will tolerate it.”

Her advice is to practise with the exact products and quantities you plan to use during an event. Race morning is not the time for your digestive system to meet a mysterious new neon-coloured gel.

4. Practise your pre-workout routine

Your brain can be involved too. Nerves and anticipation can alter gut motility, which may mean loose stools or multiple pre-race loo trips for some people.

Jackson recommends rehearsing the same breakfast, timings, fluids and sports nutrition during training.

“And we need to train the gut-brain axis as well as the muscles.”

Familiarity can help your digestive system adapt while potentially reducing some of the stress surrounding race day.

When a dodgy stomach needs medical attention

Most importantly, not every exercise-related bowel problem should simply be written off as runner's diarrhoea or IBS.

Jackson says that at the more severe end, endurance exercise has been associated with exercise-induced ischaemic colitis, where reduced blood flow to the colon causes inflammation.

Significant abdominal pain and bloody diarrhoea need medical assessment.

For everyone else, the message isn't to stop exercising, or attempt your next workout with nothing more substantial than hope in your stomach.

“My biggest advice is therefore not to simply eat less before HYROX. You need enough carbohydrate to perform and maintain your glycogen stores, while choosing foods, fluids and sports nutrition that your gut has already demonstrated it can handle. The goal is to fuel the performance without unnecessarily challenging the gut.”

Which sounds considerably more sensible than spending your entire workout mentally mapping the location of every public toilet within a two-mile radius.

About our expert

Kirsten Jackson is a Consultant Dietitian and founder of The IBS Dietitian, specialising in gut health and helping people manage digestive conditions including IBS. She also works with athletes experiencing exercise-related gut symptoms, from bloating and cramping to that dreaded mid-run dash for the loo.

Authors

Ruairidh PritchardDigital Growth Lead

Ruairidh is the Digital Lead on MadeForMums. He works with a team of fantastically talented content creators and subject-matter experts on MadeForMums.