You've likely been there: headed out on a long run only to feel some, er, digestive discomfort a few kilometres in. In fact, a dodgy belly is such a common phenomenon among regular pavement-pounders that the condition is dubbed runner's stomach.
So it's safe to say, as a newly crowned runner, I knew exactly what I was getting myself in for. I expected that my new milage would come with some stomach churning symptoms, but I didn't expect how long after the run they'd last.
You see, while there's not a lot of research around how soon a runner's stomach flare-up will ease, according to dietitian Laura Tilt, the general understanding is that it should clear up when you slow down. 'I would say that most discomfort should improve relatively quickly, either as soon as you stop running or within an hour or two,' she explains.
But for me - and many other women I've spoken to - it sometimes takes days for the bloating to go and bathroom habits to normalise. Why?
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Why do you get runner’s stomach?
'There are a number of factors at play here, but one of the key ones is reduced blood flow to the gut,' explains Laura Tilt. 'During exercise, blood flow moves away from the gut to the working muscles, lungs and skin. At high intensities blood flow to the gut can be reduced by as much as 80%, slowing gut emptying and leading to symptoms like nausea and tummy pain.'
Another reason that running impacts our digestion is because it involves literally jiggling our body - and therefore, our organs - around for hours at a time, leaving to pain and issues with gastric emptying. 'Eating too close to a run or consuming foods that are high in fibre, fat or protein is also sometimes a factor. These foods take longer to digest, meaning they might still be in the digestive system when you run. Digestion is further slowed when running, so it can lead to gastric symptoms,' adds Tilt.
"Lastly dehydration and heat stress from exercise can also impact your gut and lead to changes in gut function."
How long should runners gut last?
While there's no definitive answer to this question, running may be more likely than other forms of exercise to cause longer term tummy troubles.
'Studies of endurance athletes show that around 30-50% experience GI symptoms like acid reflux, vomiting, tummy pain and diarrhoea related to all-out exercise, although its running which is most commonly associated with gut distress, with up to 90% of distance runners experience GI symptoms,' explains Tilt.
So it's not uncommon for people training hard for long periods of time to experience longer term digestive changes. That's particularly true for people who already suffer with stomach problems: one study reported that athletes with IBS experienced more frequent symptoms during exercise as well as at rest. With an IBS diagnosis under my belt, it's perhaps unsurprising that I'm struggling with longer term runner's gut that's leaving me feeling like I'm never free from flare-ups: as soon as my stomach settles, it's time to lace again up.
Yet, I don't think being a runner and having good digestion need to be mutually exclusive, so I'm on a mission to find a way to do both.
How to ease running-induced IBS?
Any serious bloating or changes in digestion should be taken to a doctor to rule out anything more serious. But when you've worked out that it's likely your training, what can you do? Tilt has shared how to help longer term running pains: they start by figuring out your triggers, then doing trial and error with your nutrition and training.
Start with a symptom diary - if you take longer rest periods between runs do you find things are better? Does the type of run impact your symptoms? What about if you change what you eat beforehand? Make a note of it so you can begin to pair behaviour and pain.
Fuel and hydrate properly for the training you do. Both dehydration and nutrient availability can impact the gut, so start your run well hydrated and consume enough fluid when you run to limit dehydration - guidelines are around 500ml of water per hour running, and don't forget to rehydrate with sodium too. Keep bigger meals to 3-4 hours before running, and snack on simple carbohydrates an hour before you head out.
It’s important to consume 30-60 grams of carbohydrate per hour during runs lasting 60 minutes or more, but the rate and type of carbs you consume can affect GI distress. You can ‘train your gut’ to adapt to increasing amounts of carbs during running simply by practicing taking carbohydrates during your training sessions over a number of weeks with a gradual increase to a target level. If you’re unsure about how to fuel, a sports dietitian or nutritionist can help you determine which type of sports fuel will suit you best as the type and concentration of carbohydrate can impact gut comfort.
Take care with NSAIDs (non-steroidal anti-inflammatory drugs) like ibuprofen and aspirin, as these types of painkillers have been linked with an increased likelihood of gut symptoms.
If you are prone to gut symptoms, reducing fibre in the meals before your run can help, as can avoiding caffeine and spicy or high fat foods.
If you do notice high intensity exercise aggravates your gut, try stepping back on the intensity and see what happens. You should be taking regular rest in your week anyway, but a reset may be useful and long term you might find exercising at a lower heart rate more comfortable for your gut. This is particularly relevant if you have a history of gut symptoms, as studies suggest this makes you more vulnerable to GI distress.
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