What is ‘runner’s belly’ and how can you avoid it?

It’s a common phenomenon that can ruin a perfectly good run but there are things you can do to avoid runner’s belly.

If you’ve ever had to peel off for an urgent bathroom break in the middle of a nice long run, you’re far from alone.

And hear us when we say, NO-ONE wants an accident mid-race.

Known variously as “runner’s stomach”, “runner’s gut”, “runner’s belly” or “runner’s trots”, digestive disturbance while exercising — be it stomach cramping, belching, nausea, gas or an immediate need for the loo — is all too real.

What exactly is runner’s belly?

Reduced blood flow to the gut, an increase in stress hormones and the actual mechanics of running are thought to be the main causes of gastrointestinal disturbance as you run.

“During exercise blood is redirected from the gut to the working muscles,” physiotherapist and high performance director at Front Runner Sports in Perth Raf Baugh says.

“Running demands a huge amount of blood flow to extremities like your legs to fuel the exercise you’re doing which reduces blood flow to the gut, it’s a bit like the perfect storm.”

Increasing the duration of your exercise can exacerbate symptoms because it’s a longer period of time your gut isn’t getting adequate blood flow, according to advanced sports dietitian and research fellow at Monash University Steph Gaskell.

Another contributing factor may be exercise can increase your sympathetic or stress response which means your gut doesn’t absorb or digest as well, compared to when you’re more sedentary.

“When your body is more relaxed such as sitting at a desk, your digestion is pretty good because your parasympathetic nervous system is dominant over your sympathetic system, aka your fight or flight response,” Steph explains.

“The vibration and the mechanical action of running also doesn’t help sensitive tummies.”

There are also nutritional factors that can aggravate disturbance to the gut including your hydration, the timing of your last meal before exercise, the type of food you’ve eaten, feeding tolerance during exercise and gut-related medical conditions.

Who’s at risk of runner’s belly?

Research shows that anywhere between 30 to 90 per cent of runners have experienced runner’s belly.

“It’s something that no runner wants to experience but it’s incredibly common particularly in ultra-endurance events where symptoms are 60 per cent greater in comparison to less than 10 per cent in strength and power sports, team sports, and shorter duration endurance exercise,” Steph says.

“Some people are more predisposed to symptoms than others, including those with gastrointestinal conditions such as irritable bowel syndrome or inflammatory bowel disease.”

Raf says that 60 to 70 per cent of the marathon and ironman athletes he trains suffer moderate to severe gastrointestinal distress.

How can runners avoid runner’s belly?

While everyone’s symptoms are different and no one thing will work for everyone, Steph says Monash University research has shown there are a number of potential exacerbating factors involved.

“There’s no ‘one size fits all approach’ but some of things to consider are exercise intensity and duration; environmental conditions such as temperature, humidity and altitude; your sleep pattern; and the use of non-steroidal anti-inflammatories,” she says.

“Also nutritional factors including your hydration and your dietary intake including the ‘lead-in’ food and your fluid intake during exercise.”

A study from Monash University in 2020 showed that for some susceptible runners trialling a low FODMAP diet 24 hours prior to their run may help reduce the severity of symptoms.

“FODMAPs are a collection of short-chain carbohydrates that for some may not be absorbed properly in the gut and are found in a wide range of foods such as particular types of breads and cereals, certain vegetables including onion and garlic, fruits such as apples, pears and some stone fruits, some legumes and lentils and some confectionary,” Steph says.

Raf suggests runners need to “tune into their individual response to what they’re eating and make healthier choices around diet”.

“Optimise hydration and nutrition before a race and consult with a health professional to help you work out what might be triggering your issues and assist with strategies to help you avoid them,” he says.

“A qualified sports dietitian with an interest in gastrointestinal sports nutrition can save a lot of heartache for affected individuals,” Steph agrees.

Written by Liz McGrath.