Runner’s Stomach: What Causes It and How to Avoid It
Don't let digestive distress ruin your running routine. This guide explores the science behind a runner's stomach and offers practical tips to avoid it.
Updated March 18, 2024.
Ever hit the ground running, only to be sidelined by abdominal cramps and nausea? You're not alone. Runner's stomach, a common digestive issue experienced by runners, can damper your workout routine.
Imagine the frustration of training hard, only to have the body betray you mid-run. A runner's stomach can disrupt your training schedule, cause discomfort, and leave you feeling discouraged.
But a runner's stomach is preventable. By understanding it and taking some simple steps, you can keep your digestive system happy and your runs on track. Let's explore the causes and discover how to avoid it.
What is a runner's stomach?
Runner’s stomach refers to gastrointestinal (GI) symptoms such as cramping, bloating, nausea, diarrhea, vomiting, and stomach pain after running or bouts of exercise.
It likely earned its name from the sheer prevalence of runners experiencing digestive-related symptoms—an estimated 30 to 90% of distance runners, especially younger individuals, are affected by this unpleasant condition. [1, 2] Runner’s trots, runner’s belly, trot, and gut are other common names for this condition.
What do experts say?
Holley Samuel MEd, RDN, CPT, and owner of Holley Fueled Nutrition, says that many of her clients report a “sloshing in their stomach, the urgency to have a bowel movement and emergency bathroom stops while running. She also mentions that they "feel they can’t take in any hydration or fuel, before, during, or after a run."
Running isn’t the only type of exercise that can lead to these digestive symptoms, but it is the most documented. Some research suggests that team-based sports, high-intensity anaerobic drills, and sprinting can all trigger GI issues. But, only small experimental studies have attempted to investigate these relationships. [3]
How exercise triggers gut distress
- The way the gastrointestinal tract absorbs and regulates water and electrolytes changes. This prioritizes maintaining hydration throughout the body, which can impact digestion.
- Exercise stimulates the release of various gut hormones like ghrelin and leptin that influence digestion and energy availability. [4, 5]While these hormonal changes are crucial for performance, they can sometimes lead to digestive upset.
- Blood flow is strategically rerouted— exercising muscles receive a greater blood supply to meet their oxygen and nutrient demands, while blood flow to the gastrointestinal tract may be reduced. This temporary reduction can contribute to delayed gastric emptying.
- Gastric emptying, the process by which food moves from the stomach to the small intestine, slows down during exercise. This prioritizes blood flow to the working muscles and reduces the workload on the digestive system.
- Exercise can weaken the lower esophageal sphincter, a valve that prevents reflux, potentially leading to heartburn if food intake during exercise isn't managed well. [1, 2]
» Check out how to make the most out of your post-workout meal
Does high running impact make a difference?
These changes are more common during high-intensity exercise. But, the exact reasons some people experience gut issues while exercising and others aren't an area of active research. [1]
The high impact of running on the body physically jostles an already extended torso, which can lead to abdominal discomfort and stomach aches—specifically lower GI symptoms like bloating and diarrhea. [1, 2]
On the other hand, activities like cycling are a lower-impact endurance-based sport, and the position of the body is more often associated with upper-GI symptoms such as acid reflux. [2, 6]
Tip: Try slow down your pace if you experience discomfort. While this might not completely eliminate runner's stomach, it can be a simple and effective strategy to manage symptoms and let you to continue your run.
» Find out everything you need to know about your running heart rate
There's no one-size-fits-all solution for runner's stomach. While working with a dietitian or running coach can help personalize a plan, there are steps you can take to improve your gut health and optimize it for absorbing and processing pre-workout and recovery fuel. This can significantly reduce the risk of digestive issues.
InsideTracker’s gut health goal—compatible with the Ultimate plan—offers a personalized approach to optimizing your gut microbiome. It uses data from blood tests and wearable sleep trackers to create recommendations for foods, supplements, and stress management techniques that are linked to improved gastrointestinal function.
Here's how it works
InsideTracker analyzes key biomarkers, like hsCRP, a blood marker for inflammation. Research shows a two-way relationship between hsCRP and gut health. Elevated hsCRP levels may indicate poor gut health.
Based on your individual biomarker profile, InsideTracker prioritizes personalized recommendations in your action plan. For instance, you might be advised to incorporate fermented foods into your diet to improve specific gut health markers.
By getting a blood test every three to six months, you can track your progress and adjust your approach based on your body's current needs. This process lets you to continually optimize your gut health and minimize your risk of runner's stomach.
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Brief overview
InsideTracker is a personalized health and wellness platform that aims to help people optimize their biomarkers to live healthier and longer lives. It analyzes genetics, behaviors, and goals to give you personalized nutrition, fitness, sleep, stress, and supplementation recommendations.
Why choose InsideTracker
InsideTracker offers DNA testing for dozens of genetic fitness, nutrition, and longevity genetic markers. Since genetics influence many aspects of your health, the app can provide helpful context and an action plan. It also integrates with wearable devices to collect real-time health data, tracking factors like sleep, activity, and heart rate.
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Science-backed recommendations
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Encourages retesting every 3 to 6 months
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How nutrition impacts runner's stomach
Proper nutrition plays a critical role in preventing runner's stomach, the unpleasant gastrointestinal (GI) symptoms experienced by many runners. By strategically planning your meals and fueling the body appropriately, you can significantly reduce your risk of digestive distress and optimize running performance.
Timing your meals
The timing of your meals plays a crucial role in preventing runner's stomach. Certain foods, particularly when eaten too close to the start of exercise, can increase the likelihood of experiencing digestive issues.
Another common mistake is poor timing of nutrition. Taking a concentrated carbohydrate gel with a sugary sports drink can be overwhelming for some runners' digestive systems. Similarly, taking them without water can also lead to discomfort, as most gels and chews are designed to be consumed with fluids while running.
While high-carbohydrate gels and drinks provide runners with a quick energy boost, it's important to be mindful of sugar content. Too much sugar too quickly can draw excess water into the gut and potentially lead to diarrhea. [1] This applies not just to sports beverages, but also to sugary snacks you might consider pre-run.
Note: By planning your meals strategically and avoiding sugary or hard-to-digest foods close to your run, you can significantly reduce your risk of runner's stomach. Some of them, particularly when eaten too close to the start of exercise, can increase the likelihood of experiencing GI symptoms.
» Discover more about how to fuel to go the distance
What about underfueling?
Many runners, especially those new to pre-run fueling, struggle to eat before a run. Stevie highlights this point. Holly says "I hear from about 75% of my clients when we start working together that they can't tolerate or can only do so with small amounts of fuel before a run."
If you find it difficult to eat solid food before a run, consider a carbohydrate-rich sports drink as a readily absorbed source of energy. Other good pre-run options include:
- 1–2 graham cracker rectangles
- 1 applesauce packet
- 1 gel or 1 serving of sports nutrition chews
- 1 banana (or ½ the banana to start)
- 2–3 dates
- 1–2 servings of dry cereal
- 1 small cereal or granola bar (or ½ the bar to start)
- 1 serving gummy candy
- English muffin with jelly
Runners who don't meet their daily energy needs, often recommended to be higher than the average person due to their activity level, are more prone to runner's stomach. Those new to taking in fluids and food during exercise are twice as likely to develop GI symptoms compared with runners who regularly consume carbohydrates mid-run. [1]
» Dispel common myths about carb loading
Dehydration
While dehydration is not a direct cause of runner's stomach, it can significantly worsen existing symptoms. [1] Therefore, prioritizing adequate hydration throughout the day and during runs is essential for preventing gastrointestinal distress.
Sports drinks can be helpful for runners by providing electrolytes, carbohydrates, and fluids, but only for those who tolerate them well. The extra nutrients can aid digestion and performance. However, be cautious of sugar content – too much too fast can cause gut issues like diarrhea.
Tip: Stevie recommends a gradual approach to hydration: "Start with sips of water and if you can tolerate that, try to add in a sports drink to keep up on carbohydrates and electrolytes."
Supplements
Some supplements may also trigger digestive distress for individuals. Caffeine, a commonly ingested stimulant and performance enhancer, is associated with nausea during exercise. In addition, cyclists in a small study cited gut discomfort and higher perceived pain after supplementing with exogenous ketones. [7]
Other supplements including iron or magnesium also have reported GI side effects. While they are beneficial in maintaining overall health and performance for some, it may take the digestive tract time to adjust.
How to prevent runner's stomach
The best long term solution is to optimize your nutrition fueling.
In a similar way to building your running mileage, the digestive system needs to be trained to handle fuel and hydration while exercising. Practice strategic pre-run fueling, proper timing of in-run nutrition, and gradually training the gut to tolerate food and fluids during exercise.
Start small with easily digestible carbohydrates—low in fiber—20–40 minutes before a morning run. A serving size could be around 15–20 grams of carbohydrates, which is roughly half of a large banana. As your gut adjusts, you can gradually increase the amount you take pre-run.
For workouts that don't happen right after waking up, Holley suggests reducing fiber and fat content in the previous meal—lunch or dinner—and incorporating a small carbohydrate-rich snack 30–60 minutes before your run.
Note: Everyone's digestive system is different. If you experience persistent GI distress despite implementing sound nutrition practices, or if you have significant pain or blood in your stool, consult a doctor to rule out other potential causes.
Silence your stomach rumbles
Runner's stomach can significantly impact your running performance. While the exact causes vary, a combination of factors like reduced blood flow to the digestive system, hormonal changes, and food choices can contribute to these unpleasant symptoms.
The good news is that runner's stomach is largely preventable. By strategically planning your meals, staying hydrated, and experimenting with different pre-run fueling options, you can train your gut to handle exercise and reduce your risk of digestive issues.
To address runner's stomach, InsideTracker offers a gut health goal specifically aimed at improving the microbiome. Based on the analysis of your blood biomarkers, you'll get personalized and science-backed recommendations to optimize your health and live healthier and longer.
InsideTracker doesn't diagnose medical conditions. For any health-related concerns, consult your physician.
References:
[1] E. P. De Oliveira, R. C. Burini, and A. E. Jeukendrup, “Gastrointestinal complaints during exercise: prevalence, etiology, and nutritional recommendations,” Sports Medicine, vol. 44, no. S1, pp. 79–85, May 2014, doi: 10.1007/s40279-014-0153-2.
[2] “UpToDate,” UpToDate. https://www.uptodate.com/contents/exercise-related-gastrointestinal-disorders#H3
[3] P. B. Wilson, “Frequency of chronic gastrointestinal distress in runners: Validity and reliability of a retrospective questionnaire,” International Journal of Sport Nutrition and Exercise Metabolism, vol. 27, no. 4, pp. 370–376, Aug. 2017, doi: 10.1123/ijsnem.2016-0305.
[4] N. Ouerghi et al., “Ghrelin Response to Acute and Chronic Exercise: Insights and Implications from a Systematic Review of the Literature,” Sports Medicine, vol. 51, no. 11, pp. 2389–2410, Aug. 2021, doi: 10.1007/s40279-021-01518-6.
[5] “Leptin, its implication in physical exercise and training: a short review,” PubMed, Jun. 01, 2006. https://pubmed.ncbi.nlm.nih.gov/24259989/[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4281377/
[7] J. J. Leckey, M. L. Ross, M. Quod, J. A. Hawley, and L. M. Burke, “Ketone diester ingestion impairs Time-Trial performance in professional cyclists,” Frontiers in Physiology, vol. 8, Oct. 2017, doi: 10.3389/fphys.2017.00806.
