For many runners, stomach trouble is an unfortunate yet familiar part of the sport. Whether it’s nausea, cramping, bloating, or an unexpected dash to the nearest restroom, gastrointestinal (GI) distress can derail even the best training plans. Known as “runner’s stomach,” this condition affects athletes of all levels, from casual joggers to elite marathoners.

But what exactly causes runner’s stomach, and how can it be prevented? The interplay between exercise, digestion, hydration, and nutrition makes this a complex issue, but understanding the underlying factors can help athletes manage and minimize symptoms. This article delves into the causes of runner’s stomach, explores treatment options, and offers practical strategies for prevention.

What Is Runner’s Stomach?

Runner’s stomach refers to a set of exercise-induced gastrointestinal symptoms that occur during or after running. These symptoms can include:

• Nausea
• Stomach cramps
• Diarrhea
• Vomiting
• Acid reflux
• Bloating

Studies suggest that 30% to 90% of endurance athletes experience some form of GI distress, with runners particularly affected due to the high-impact nature of the sport [1, 2].

What Causes Runner’s Stomach?

The exact cause of runner’s stomach varies from person to person, but researchers have identified several physiological and nutritional factors that contribute to GI distress during exercise.

1. Reduced Blood Flow to the Digestive System

During exercise, the body prioritizes blood flow to working muscles, meaning less blood is available for digestion. This reduced circulation can impair the stomach’s ability to break down food, leading to discomfort and bloating [3].

2. Increased Gut Permeability

Strenuous exercise, especially long-distance running, increases the permeability of the intestinal lining. This means bacteria and toxins can leak into the bloodstream, triggering inflammation and diarrhea—sometimes referred to as “leaky gut syndrome” in athletes [4].

3. High-Impact Jostling

Unlike cycling or swimming, running involves repeated up-and-down motion, which physically shakes the digestive system. This mechanical movement can lead to stomach cramping and urgency, particularly for those already prone to GI issues [2].

4. Hormonal Changes

Exercise affects gut hormones like ghrelin (which stimulates hunger) and leptin (which signals fullness). These fluctuations can slow digestion and cause nausea or discomfort, especially during prolonged runs [5].

5. Dehydration and Electrolyte Imbalance

When the body loses fluids through sweat, it also loses key electrolytes like sodium and potassium. Dehydration can lead to cramping and slowed digestion, exacerbating runner’s stomach [1].

6. Poor Pre-Run Nutrition Choices

Eating high-fat, high-fiber, or overly sugary foods before running can increase the likelihood of GI distress. Certain sports drinks, gels, and supplements may also be culprits due to their high sugar or caffeine content [6].

How to Prevent Runner’s Stomach

While some degree of digestive discomfort is unavoidable in endurance sports, several strategies can help reduce the risk of runner’s stomach.

1. Optimize Pre-Run Nutrition

• Time Your Meals: Eat at least 2 to 3 hours before running to allow digestion to complete.
• Choose Low-Fiber, Low-Fat Foods: Avoid foods that slow digestion or cause bloating, such as beans, dairy, and greasy meals.
• Be Mindful of Sugar and Caffeine: While some runners tolerate sports gels, energy drinks, or coffee, others find they trigger GI distress. Experiment during training runs to identify your tolerance.

2. Stay Hydrated—But Not Too Much

• Drink small amounts of water consistently throughout the day, rather than overloading right before a run.
• Balance electrolytes by incorporating sodium-rich foods or electrolyte tablets if running in hot conditions.

3. Train Your Gut

Research suggests that runners who regularly consume carbohydrates during training sessions experience fewer GI symptoms in races. Gradually introducing mid-run fueling—such as sports drinks, chews, or small snacks—can help your gut adapt [7].

4. Adjust Running Intensity

High-intensity workouts put more stress on the digestive system. If you experience symptoms frequently, try slowing your pace or adjusting your effort level.

5. Avoid NSAIDs and Certain Supplements

Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen can increase gut permeability, making symptoms worse. Supplements like iron, magnesium, and exogenous ketones may also contribute to GI distress for some runners [8].

How to Relieve Runner’s Stomach Symptoms

If symptoms strike mid-run or after exercise, try these recovery strategies:

• Sip water or an electrolyte drink to restore hydration.
• Walk or slow down to ease cramping.
• Try ginger or peppermint tea to soothe nausea.
• Eat a bland snack (like toast or crackers) to settle the stomach.
• If diarrhea occurs, avoid dairy and high-fat foods for the next few hours.

If symptoms persist frequently despite lifestyle changes, consult a doctor to rule out underlying conditions like irritable bowel syndrome (IBS) or food intolerances.

Conclusion

Runner’s stomach is a common but manageable issue that affects many athletes. By understanding the physiological changes that occur during exercise and making strategic adjustments to nutrition, hydration, and training, runners can minimize their risk of GI distress. The key is to experiment with different strategies and find what works best for your body.

With the right approach, stomach troubles don’t have to slow you down.

References

1. De Oliveira, E. P., Burini, R. C., & Jeukendrup, A. E. (2014). Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations. Sports Medicine, 44(S1), 79–85. doi:10.1007/s40279-014-0153-2
2. UpToDate. (n.d.). Exercise-related gastrointestinal disorders. Retrieved from https://www.uptodate.com
3. Wilson, P. B. (2017). Frequency of chronic gastrointestinal distress in runners: Validity and reliability of a retrospective questionnaire. International Journal of Sport Nutrition and Exercise Metabolism, 27(4), 370–376. doi:10.1123/ijsnem.2016-0305
4. Ouerghi, N., et al. (2021). Ghrelin Response to Acute and Chronic Exercise: Insights and Implications from a Systematic Review of the Literature. Sports Medicine, 51(11), 2389–2410. doi:10.1007/s40279-021-01518-6
5. Leptin and physical exercise: A review. PubMed, (2006). Retrieved from https://pubmed.ncbi.nlm.nih.gov
6. Morton, D., & Callister, R. (2014). Exercise-Related transient abdominal pain (ETAP). Sports Medicine, 45(1), 23–35. doi:10.1007/s40279-014-0245-z
7. Leckey, J. J., et al. (2017). Ketone diester ingestion impairs Time-Trial performance in professional cyclists. Frontiers in Physiology, 8. doi:10.3389/fphys.2017.00806