Exercise doesn’t just build stronger muscles or help your heart pump more efficiently. It can also support gut health. Except this isn’t always the case. If you’ve ever experienced bloating, nausea, cramps, reflux, or urgency during or after a long, intense session, you’re not alone.

We don’t often think about how exercise affects the gut. However, it’s where you absorb the nutrients needed for recovery, as well as the fluid you lose through sweating. Gut health for athletes is therefore crucial.

A big part of how effectively your gut functions is the microbiome: the community of microorganisms living inside it. If disrupted, it may affect everything from digestion and recovery to athletic performance. A simple gut microbiome test can help you understand what’s going on.

How Does Exercise Affect Gut Health?

Exercise is mostly good for the gut. It supports bowel motility, metabolic health, and microbial function. The latter is quite important.

One systematic review found that exercise could improve microbial diversity, a key marker of gut health, although over half the studies in the review found no significant effect.

People who exercise regularly are also more likely to look after their health. Diet, body composition, training history, and exercise type mean it’s difficult to isolate exercise as the cause. But the evidence does indicate some beneficial effects.

Why Does Exercise Cause Gut Symptoms?

Reduced Blood Flow

Exercise gets the blood pumping. The harder you work, the more intensely the blood pumps. Unfortunately for the gut, much of the blood is redirected from the digestive system towards the working muscles and skin.

Heat and dehydration can further reduce blood flow, potentially affecting absorption and gut barrier function. It’s one of the primary reasons people experience gut symptoms after a particularly intense session.

Mechanical Stress

Take anything and shake it around for an hour. Some disruption is to be expected. Your body is no different.

Running, for example, repeatedly jolts the digestive system. It may explain why runners often experience more symptoms than cyclists. Movement can contribute to urgency, abdominal discomfort, and diarrhoea.

Food and Fluid Intake

Exercise makes us hungrier. The problem is that large meals, concentrated carbohydrate drinks, and foods high in fat or fibre shortly before training can slow digestion or worsen symptoms.

Diet also impacts microbial composition.

Exercise-induced gastrointestinal symptoms are usually caused by several factors rather than one unhealthy food or bacterial species. It’s the combination of factors that matters.

How Training Load Can Change the Gut Microbiome

Not all training is the same.

Moderate, consistent training is associated with beneficial microbial changes. Heavy training blocks, on the other hand, produce different effects, especially when combined with heat, inadequate recovery, disrupted sleep, or under-fuelling.

Training-related changes in diet also matter.

Resistance training often goes alongside protein supplements or periods of restricted eating, while runners can load up on carbs to increase calories. Together, these factors gradually alter microbial composition, favouring certain species over others.

Why Endurance Athletes Are a Distinct Group

Runners, cyclists, triathletes, and other endurance athletes are in a class of their own. The extraordinary pressures the body endures place unusual demands on their digestive systems.

Not only must they absorb large amounts of fluid and carbohydrates, but blood flow to the gut is also reduced during a training session.

Add in hotter temperatures, repeated consumption of gels, drinks, or solid food, and even dehydration, and it’s clear why symptoms can be more common.

How Athletes Can Protect Their Gut Health

You don’t need to give up exercise if you’re experiencing symptoms. A few sensible changes can help preserve your gut health:

• Practise consuming race-day fluids, carbohydrates, and gels during training.

• Avoid large, high-fat, or high-fibre meals shortly before intense exercise.

• Start each session hydrated and replace fluids appropriately.

• Eat enough to support training and recovery.

• Track food, exercise, and symptoms before eliminating potential triggers.

When Should an Athlete Consider Gut Testing?

Testing isn’t always necessary. Most athletes can respond to slight changes in their training routine or lifestyle. However, if symptoms are persistent, recurrent, or severe enough to affect fuelling, performance, or recovery, it’s time to think about a gut health test.

The Functional Gut Clinic can help athletes take control of their gut health. We offer a range of testing options that can help you understand your microbial composition and diversity, providing concrete advice on how to support your gut.

Learn more about our testing options and take control of your health.

Read the next article: What Your Stool Says About Your Gut