runner’s gut: what it is, why it happens, and how to beat it

Runner’s Gut: What It Is, Why It Happens, and How to Beat It

Runner’s gut – also known as runner’s stomach or the dreaded runner’s trots – is a common issue affecting many athletes. But why does it happen, and what can you do to prevent it?

What Is Runner's Gut?

Runner’s gut refers to a range of gastrointestinal (GI) issues triggered by running. Symptoms can include cramping, bloating, nausea, acid reflux, and diarrhoea. While it’s most common in long-distance runners, it can affect athletes at any level.

Why Does It Happen?

There are a few key reasons why running can cause stomach and bowel problems:

1. Reduced blood flow

During exercise, blood is redirected away from the digestive system to fuel working muscles. This can slow digestion, cause discomfort, and accelerate gut transit time—leading to an urgent need for the toilet.

2. Stress and the fight-or-flight response

Running, particularly at high intensities or in race settings, triggers a surge of adrenaline. This stress response can speed up digestion, sometimes leading to sudden bowel urgency. Pre-race nerves can also make symptoms worse.

3. Dietary triggers

Certain foods and supplements commonly used by runners can exacerbate gut issues:

• Carbohydrate loading – Excess refined carbs before a run can overwhelm digestion.

• Energy gels and sports drinks – High in sugars and artificial ingredients, these can upset the stomach.

• Caffeine – While it enhances performance, it can also act as a laxative.

• Medications – NSAIDs (such as ibuprofen) and proton pump inhibitors (for acid reflux) may irritate the gut.

Impact of Running on the Gut

Intense training can lead to gut imbalance and barrier weakness. When the gut microbiome is disrupted, the balance of gut bacteria is altered, creating an environment where harmful microbes can thrive. Additionally, extreme physical exertion can weaken the intestinal barrier, making it more permeable. This weakened barrier compromises its ability to protect against harmful substances, potentially leading to further health issues. The gut barrier, made up of tightly joined cells, protects the body by controlling what enters the bloodstream. Intense training can weaken this barrier by disrupting the tight junctions between cells, making the gut more permeable. This allows harmful substances, like toxins and bacteria, to leak into the bloodstream, triggering inflammation and potentially leading to digestive and immune system issues.

How to Prevent Runner’s Gut

The good news is that there are a few things you can do to prevent runner’s gut:

1. Time your meals
   Try giving yourself at least two to three hours to digest before you head out for a run. Everyone’s different, so experiment a bit to see what timing works best for you.

2. Choose gut-friendly foods
   Before a run, steer clear of high-fibre, high-fat, and overly processed foods. Instead, go for easy-to-digest carbs with a little protein to fuel you without upsetting your stomach.

3. Stay hydrated
   Dehydration can lead to cramping, so make sure to sip fluids throughout your run to stay hydrated.

4. Manage stress
   Nerves before a race or run can trigger gut issues, so try to relax with deep breathing, meditation, or visualization techniques to keep your stress in check.

5. Use probiotics to support gut health
   Interestingly, balancing the gut’s microbiome with helpful bacteria like Bifidobacterium, and Lactobacillus could help strengthen the gut barrier. This helps keep the gut lining stable and intact, which may protect against issues caused by intense exercise, such as gut discomfort and inflammation.

Conclusion

Runner’s gut can be a frustrating issue, but it doesn’t have to derail your training. With a combination of smart fuelling, hydration strategies, gut support, and stress management, you can keep GI problems at bay and focus on what truly matters – enjoying your run.

References

1. Pugh, J., Sparks, A., Doran, D., Fleming, S., Langan-Evans, C., Kirk, B., Fearn, R., Morton, J., & Close, G. (2019). Four weeks of probiotic supplementation reduces GI symptoms during a marathon race. European Journal of Applied Physiology.
2. Ribichini, E., Scalese, G., Cesarini, A., Mocci, C., Pallotta, N., Severi, C., & Corazziari, E. S. (2023). Exercise-induced gastrointestinal symptoms in endurance sports: A review of pathophysiology, symptoms, and nutritional management. Dietetics, 2(3), 289-307. https://doi.org/10.3390/dietetics2030021
3. Smarkusz-Zarzecka, J., Ostrowska, L., Leszczyńska, J., & Cwalina, U. (2022). Effect of a Multi-Strain Probiotic Supplement on Gastrointestinal Symptoms and Serum Biochemical Parameters of Long-Distance Runners: A Randomized Controlled Trial. International Journal of Environmental Research and Public Health.