Runner's Diarrhoea: Causes & Prevention Tips

Just a few weeks ago, whilst looking out of my window with a hot cup of tea, I saw thousands of people running past, taking part in the Brighton marathon. Along with thoughts such as "I wonder how long they've been running for" and "my knee's would never let me do that", I found myself wondering about how their bowels are doing.

Runner’s diarrhoea; unpleasant, potentially embarrassing and more common than you might think. Endurance athletes are most likely to experience runner’s diarrhoea; it is extremely prevalent within this community due to the type of exercise they are doing. 

The lovely Paula Radcliffe, an experienced endurance runner, suffered with runner’s trots during the 2005 London Marathon.1 Whilst running, she felt the urgent need to go so decided to poop in her pants; the only option if she wanted to continue with the race. We LOVE the dedication to her sport, yet also hope she never has to experience that again! 

It’s currently marathon season, and with the London marathon approaching on the 23rd of April, we wanted to chat about runner’s diarrhoea, explain what it is, how it happens and give some advice on how to prevent it from happening to you. 

What is Runner's Diarrhoea?

Runner’s diarrhoea, or runner’s trots, is frequent loose bowel movements either during or immediately after running.2 It most commonly occurs in long distance runners, hence why it is important to discuss during marathon season! 

Runner’s diarrhoea usually won’t last for more than 24 hours, unlike other causes of diarrhoea which often last longer. Other symptoms include nausea, acid reflux, cramping and excess gas. One study found that 62% of long distance runners have reported having to stop running to have a bowel movement, showing a huge link between running and the urgent need to go.5

Suffering from runner’s diarrhoea can cause emotional distress; some find it embarrassing or shocking when it happens to them, and it can affect their desire to continue running in the future. Sharing some preventative measures could help to put your mind at ease, so that you can limit your chances of getting runner’s trots. 

Causes of Runner's Diarrhoea

It’s common for endurance atheletes, including runners, to experience gastrointestinal issues such as nausea, bloating, cramping, diarrhoea and vomiting when carrying out high intensity exercise. This is known as exercise-induced GI distress, and can happen to anyone.3

Unfortunately, the exact cause of runner’s diarrhoea isn’t particularly clear. Many factors could be contributing to runner’s trots, all caused by the act of running itself. 

Whilst running, physically, you will experience a decreased blood flow to your intestines, changes in hormone secretion, and your organs will be jostled around.2 These physical factors could contribute to runners diarrhoea, as blood flow, stability and normal hormone secretion are all important for the digestive system to run smoothly. 

Whilst completely high intensity exercise, up to 80% of the blood supply going to the gut is instead sent to the exercising muscles and organs. This means that the gut isn’t getting enough blood during the exercise to function properly, and can cause damage to the cells through a lack of oxygen, which can cause diarrhoea.4

The food you eat before running could also have an impact. If you have just eaten a new food that your body is struggling to digest, or eaten a large amount of food, this could lead to runner’s diarrhoea. Food moves more quickly through the bowels of training athletes, so eating too soon before a race could lead to runner’s trots.2

Pre-race anxiety and stress is super common amongst runners, particularly in organised events.2 This anxiety and stress is likely to have a hand in runner’s diarrhoea; check out our article Introduction to Gut Health and Stress to learn more about this area!

Dehydration could play a part in runner’s diarrhoea, too. Hydration is essential for the digestive system to function properly, and when you run, you often lose fluid at a rapid rate. Dehydration can cause diarrhoea, as fluid is needed to properly move food through the gastrointestinal tract, and without it, the bowels can become distressed. 

Prevention Strategies for Runner's Diarrhoea

As we know, the food you consume before a race can be a contributing factor to runner’s diarrhoea. At least one day before, limit or avoid foods that are high in fibre. Although fibre is important for digestion and gut health, before a run is not the best time to consume them. If you are an every day runner, experiment to find a tolerable level of fibre that works for your body. Otherwise, simply eat those foods after you run.

At least one day before you run, limit or avoid eating sweeteners. These can act as a laxative, which makes them more likely to induce diarrhoea. 

In the six hours before running, limit or avoid caffeine and high-fat foods. These foods are digested quickly, meaning they pass through you faster than other foods. Save caffeine and high-fat foods for post-run! 

For at least two hours before completing your run, don't eat anything at all. This will ensure your body isn’t fighting to digest with 80% less blood flow, and whilst being shaken up and down as you run. 

Before, during and after your run, drink plenty of fluids. As we know dehydration can lead to diarrhoea, staying hydrated is crucial. Whilst choosing your fluid, avoid warm liquids, as they can speed food through the digestive tract.

While running, limit your use of energy gels and bars, as these products can contribute to diarrhoea in some people. In particular, avoid introducing a new gel or bar on race day, as you don’t know how your body will react to the particular gel or bar. Try them out before you run!

This may seem obvious, but is worth mentioning. If you're lactose intolerant, don't consume lactose, and instead consume lactose-reduced or free products. If you have any other food intolerance, avoid eating those foods, particularly in the days leading up to your race. Food intolerance symptoms don’t always happen immediately after eating the food, so better safe than sorry on this one. 

Avoid nonsteroidal anti-inflammatory drugs on race day. Anti-inflammatory drugs have been shown to increase the incidence of gastrointestinal complaints, so are not a good choice before or during a run. 

Wearing comfortable clothing that isn’t too tight when running can help to prevent diarrhoea. Tight clothing on the abdomen may aggravate the stomach and lead to diarrhoea. 

Make sure you have properly trained your gut for the run! Training your gut to cope with high-intensity exercise is just as important as training the muscles of your body. Gradually increasing the intensity and duration of your runs, rather than jumping straight into endurance running, can give your gut time to adapt. 

Finding ways to manage your pre-run stress and anxiety could go a long way to preventing runner’s diarrhoea. Meditation, deep breathing and yoga could all be beneficial for getting you in a calm head space before completing your run. Finding a calming technique that works for you is important, so experiment with different methods of relaxation! 

If you are suffering from runners diarrhoea, over-the-counter or prescription medications could help to alleviate symptoms. Talk to your doctor or a pharmacist for advice based on your specific circumstances to find the right treatment for you. 

If you need help with GI stress during exercise or marathon preparation, why not book in for a consultation with our expert sports nutritionist? Email to book in for an online consultation with Abi. 

Take Home Message

Runner’s diarrhoea is nothing to be ashamed of; it can happen to anyone that partakes in high-intensity exercise, and is no reflection on your athletic ability. It may be worth following our preventative steps to help limit your chances of getting runner’s diarrhoea, and knowing the potential causes can help to educate yourself on what’s happening in your body whilst completing endurance exercise. 

Runner’s diarrhoea is a manageable problem that doesn’t have to derail your marathon goals. If you have any concerns, don’t hesitate to talk to a medical professional, or book in for a consultation with our sports nutritionist! 

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