Is too much exercise bad for your gut?

Two new studies have been published, linking intense, prolonged exercise to gut problems and changes to gut bacteria.

One of the studies suggests that exercising hard for more than two hours could be dangerous for your intestines and bowel, and increase the risk of gut problems. The other adds support to the idea that intense physical exercise causes big changes to the bacteria in your gut. In this post, we’ll take a closer look at the evidence, and what it means for you.

The studies

One of the new studies was carried out by Australian sports scientists. They found that strenuous exercise can damage intestinal cells, leading to short- and long-term gut problems. The damaged tissue can then cause toxic substances to leak out of the intestines and into the bloodstream. The researchers found that exercising in high temperatures can exacerbate these effects.

Exercise and stomach problems

One of the new studies was carried out by a team of researchers in Norway, studying a group of soldiers on a training exercise. They found that the soldiers’ urine showed a significant increase in the amount of sucralose after the intense training period. 

This supports the evidence from the Australian study suggesting that the gut wall becomes more permeable, and more prone to ‘leaks’, during prolonged periods of intense exercise. This is commonly known as ‘leaky gut syndrome’.2

The researchers also found that the gut bacteria and metabolites in the soldiers’ bodies changed significantly by the end of the intense training period. This shows that prolonged intense exercise can have a big impact on the microbiome, as well as the body’s ability to metabolise food.2

What it means

The two main findings by these studies have significant implications for gut health and exercise, both for people with healthy digestion and those with existing conditions such as IBS.

Leaky gut syndrome

Healthy intestines have a semi-permeable barrier which keeps harmful substances out while allowing nutrients into the bloodstream. However, if this barrier becomes damaged it can allow toxic substances to leak from the intestines into the bloodstream. Scary as this sounds, there is currently not much evidence that this ‘syndrome’ is the direct cause of any other significant health problems.3

Changes to gut bacteria 

The microbiome is the body’s gut bacteria, which digests food and supports the immune system by manufacturing vitamins including K and B12. Metabolites are a substance formed in the gut which is important in turning food into energy. Both studies suggest that prolonged intense exercise upsets or alters the microbiome and metabolites. Poor gut health is increasingly being linked to a wide range of conditions including diabetes, obesity and high blood pressure.2

This research should not be taken as a warning not to exercise. Whether you have an existing condition such as IBS or whether your gut is completely healthy, regular, moderate exercise has many health benefits. The Australian study stated that gut problems appeared at a certain threshold, which was two hours of exercise in one go at 60% of maximum effort. 

Exercising below this threshold carries all the health benefits without compromising gut health or integrity.1 However, some people do experience gut symptoms (such as nausea, bloating, heartburn, cramps or flatulence) during exercise at any level of intensity, known as “exercise-induced gastrointestinal syndrome”. If you experience this, we recommend getting an assessment of your gut health in order to work out what is causing it. 

Exercise and stomach problems

It could be a sign of underlying gut problems, which are exacerbated by exercise.

Endurance athletes and military personnel, such as those included in the Norwegian study, are at a higher risk of experiencing these symptoms. 96% of ultra-marathon runners and 93% of ironman triathletes report gut symptoms while training or racing.1

If you are concerned about gut health or you want to find out more about the related conditions, click through to read these consultant Q&As on bowel cancer and irritable bowel syndrome and our insightful article on why you should listen to your gut.

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