Doctor explains why most marathon runners always need the bathroom at mile 18

As people are doing their final preparations ahead of the London Marathon, a gastroenterologist named Dr Trisha Pasricha has shared the reason why many runners will need the bathroom at mile 18

As many people are preparing to run the London Marathon on 26 April, one gastroenterologist has shared the reason a lot of marathon runners will often need to run to the nearest toilet at mile 18 of the race.

Whether you’re an experienced runner or someone who’ve just started out, chances are you might have experienced something called ‘runner’s trot’. This is the moment during or after a run when you get a urge to rush to the bathroom for a sudden bowel movement. While it may appear odd if you haven’t heard of it before, it’s a very common thing that often happens when someone is in the middle of or has just finished an intense run – such as a marathon.

To explain this further, Harvard doctor and scientist Dr Trisha Pasricha, who is also the author of bestselling book ‘You’ve Been Pooping All Wrong’, explained what happens in your gut when you’re running, which leads to people rushing to the nearest loo at around mile 18 of a marathon.

“Why do so many marathoners suddenly need to use the bathroom in the middle of the race?” she wrote at the caption of her Instagram post. She went on to explain the phenomenon more in her video.

“When you run, blood flow to your gut can drop to 20% of its baseline,” she explained. “That is literally just your body choosing your legs over your intestines.”

She continued to explain this is the reasons why so many runners, when they hit mile 18 struggle to keep anything down. Runners often start to feel ill and have to run to the bathroom because of it.

“Your gut is screaming that it is not getting enough blood,” Dr Pasricha said.

But there are ways to predict this, especially if you’re wearing a smart watch or another type of fitness tracker. This is because the symptoms tend to cluster when a runner’s heartrate hits a certain threshold.

“So when you’re training, pull up that heart rate date and see ‘how high does it go before I start to get symptoms?’” she recommended. You can then use the answer to help recalibrate your training goals to help stick below that threshold.

Dr Pasricha also urged runners to stay hydrated, but to keep away from sugary beverages. Instead, she recommended to use electrolytes to boost hydration throughout the race.

“Honestly, I’d probably skip the coffee the morning of the race too,” she said, claiming it would ‘rev up your colon’, while she said you should aim for it to be as calm as possible before and during your race. She added in the caption of her post: “If you know, you know.”

Several runners soon took to the comment section of the video to share their gratitude to the gut doctor for explaining the phenomenon to them.

“Ah, thank you. Another reason half marathons seem like a better option,” one person said. Someone else wrote: “Thanks for this information!”