Any gastrointestinal issue can interfere with your running more than you might expect. Nausea, gas, diarrhea, or constipation—when your GI system acts up, even mild symptoms can throw your workout completely off track.
Runner’s stomach, often called runner’s gut, is one of the most common culprits. It can trigger bloating, cramps, nausea, or diarrhea during runs, making training and racing feel much harder than they should.
As both a running and nutrition coach, I see this problem frequently in athletes, and the solution often starts with dialing in a personalized fueling plan.
In this guide, we’ll break down what runner’s stomach is, the most common causes behind it, and proven strategies to treat and prevent it so you can keep your runs strong and symptom-free.
What Is Runner’s Stomach?
Runner’s stomach is a loose term that describes various gastrointestinal symptoms while running, such as abdominal pain, cramping, nausea, diarrhea, gas, bloating, an upset stomach, the urgency to use the bathroom, belching, and side stitches.
You may also experience stomach pain after running.
Experts suggest1ter Steege, R. W. F., & Kolkman, J. J. (2012). Review article: the pathophysiology and management of gastrointestinal symptoms during physical exercise, and the role of splanchnic blood flow. Alimentary Pharmacology & Therapeutics, 35(5), 516–528. https://doi.org/10.1111/j.1365-2036.2011.04980.x that runner’s stomach can be caused by the actual jostling and mechanics of the running motion, as well as dietary, hydration, training, and hormonal factors.
Studies have found2Samborski, P., Chmielarz-Czarnocińska, A., & Grzymisławski, M. (2013). Exercise-induced vomiting. Przegla̜d Gastroenterologiczny, 8(6), 396–400. https://doi.org/10.5114/pg.2013.39924 that up to 83% of marathon runners have gastrointestinal complaints associated with their running.
The Real Reasons Behind Stomach Pain While Running
Several factors can contribute to Runner’s Stomach, and often it’s a combination rather than just one culprit.
Eating too close to a workout is a common trigger, since food that hasn’t had enough time to digest can lead to cramping once you start moving.
Similarly, consuming sugary drinks or high-carbohydrate foods before running has been shown to increase the risk of stomach cramps.3Morton, D., & Callister, R. (2014). Exercise-Related Transient Abdominal Pain (ETAP). Sports Medicine, 45(1), 23–35. https://doi.org/10.1007/s40279-014-0245-z
Hydration habits also play a role—both dehydration and drinking water too quickly can cause uncomfortable bloating during a run.
The type of food you choose matters as well: fatty, high-fiber, or protein-heavy meals delay gastric emptying, making you feel weighed down and more prone to stomach distress.
In addition to nutrition and hydration, running intensity and breathing mechanics can exacerbate the problem. Pushing the pace too hard or breathing unevenly can put extra strain on the diaphragm, a key muscle involved in both breathing and core stability, which may further aggravate stomach pain.
Effective Strategies for Preventing Runner’s Stomach
Digestive distress while running is common, but the good news is that there are proven ways to reduce or even prevent it. Here are my top effective strategies to help keep your stomach calm so you can focus on your miles:
#1: Eliminate foods that cause bloating
Certain foods trigger bloating more than others, depending on your digestive system. Common culprits include high-fiber foods, fatty meals, dairy (if you’re lactose intolerant), and foods high in FODMAPs like onions, garlic, and cauliflower.4de Oliveira, E. P. (2017). Runnerʼs diarrhea. Current Opinion in Gastroenterology, 33(1), 41–46. https://doi.org/10.1097/mog.0000000000000322
Carbonated drinks, salty processed foods, and even chewing gum can also contribute to bloating and discomfort.
Keep a food journal to identify your own triggers, and consider working with a sports dietitian for a tailored plan.
#2: Rethink your hydration
Both dehydration and drinking too much water at once can lead to stomach issues.
Find your sweat rate by weighing yourself before and after a run to better understand your fluid needs.
How to do a simple sweat test:
- Weigh yourself with no clothes or shoes on before your run.
- Run for 60 minutes at your usual training effort.
- Do not drink any fluids during the test.
- After the run, towel off and weigh yourself again, no clothes or shoes.
- Subtract your post-run weight from your pre-run weight to find how much fluid you lost.
Example:
If you weighed 150 lbs before your run and 149 lbs after, you lost 1 pound (16 ounces) of fluid in 1 hour. That means your sweat rate is 16 ounces per hour.
While running, try to replenish a good percentage of your fluid loss by sipping small amounts regularly instead of chugging.
During exercise, it is usually best to take in fluids periodically and gradually, so that you do not overload your system with water all at once, which can lead to uncomfortable bloating and sloshing in your stomach, and decrease the absorption rate of your fluids.
Therefore, a good hydration strategy should be planned out for the fluid portion of hydration needed during exercise. For our example subject, they would need to drink about 4 ounces of water5McDermott, B. P., Anderson, S. A., Armstrong, L. E., Casa, D. J., Cheuvront, S. N., Cooper, L., Kenney, W. L., O’Connor, F. G., & Roberts, W. O. (2017). National Athletic Trainers’ Association Position Statement: Fluid Replacement for the Physically Active. Journal of Athletic Training, 52(9), 877–895. https://doi.org/10.4085/1062-6050-52.9.02 every 15 minutes during the run.
On hotter days, this should be adjusted up to 6 ounces or so, depending on the temperature difference between the two conditions.
Consider adding electrolytes and glucose to your water, or use sports drinks, especially if your workout lasts more than 90 minutes.
Studies have shown6Millard-Stafford, M., Snow, T. K., Jones, M. L., & Suh, H. (2021). The Beverage Hydration Index: Influence of Electrolytes, Carbohydrate and Protein. Nutrients, 13(9), 2933. https://doi.org/10.3390/nu13092933 that drinking plain water causes people to feel more bloated than drinking electrolyte—or carbohydrate-infused beverages.
Plus, there is a large body of evidence7Orrù, S., Imperlini, E., Nigro, E., Alfieri, A., Cevenini, A., Polito, R., Daniele, A., Buono, P., & Mancini, A. (2018). Role of Functional Beverages on Sport Performance and Recovery. Nutrients, 10(10), 1470. https://doi.org/10.3390/nu10101470 that has found that sports drinks that combine carbohydrates (particularly glucose and fructose) with electrolytes can improve athletic performance by optimizing the absorption of water and electrolytes and maintaining metabolism.
According to research, the ideal concentration of carbohydrates in these electrolyte drinks is 6-8%. For workouts lasting over 90 minutes, the overall goal is to ingest 30–90 grams of carbohydrates per hour.
#3: Wait long enough after eating
It’s common to experience digestive issues if you run too soon after eating.
Plan to wait about 3-4 hours to run after eating a large meal, 2-3 hours for a small meal, and 1-2 hours after most snacks unless it’s a tiny snack consisting of only simple carbohydrates (like a gel) and you’re doing a very low-intensity, slow recovery run.
#4: Slow your breathing
Shallow, uneven breathing can put strain on your diaphragm and contribute to cramps. Practice a 3:2 breathing pattern—inhale for three steps, exhale for two—and focus on deep belly breaths to maintain stable oxygen flow and core strength.
#5: Pace yourself early
Starting too fast increases physical stress on your body, including your digestive system. Warm up and begin runs at a controlled pace to give your gut time to settle before gradually building effort.
#6: Practice your fueling in training
Never introduce new gels, chews, or sports drinks on the day of the race.
Instead, train your gut by practicing with the exact nutrition plan you’ll use in competition. Over time, your digestive system adapts and becomes more efficient at handling fuel while running.
#7: Stick to consistent pre-run routines
Your digestive system thrives on routine. Try to eat similar foods, in similar portions, at consistent times before runs, especially before long runs and races. This predictability helps your stomach know what to expect.
#8: Manage pre-race nerves
Anxiety can speed up or disrupt digestion, leading to cramps or diarrhea on race day. Use calming strategies, such as deep breathing, meditation, or a familiar warm-up routine, to help keep nerves under control and reduce stress-related stomach upset.
Digestive distress is a common challenge for runners, and as we’ve seen, stomach cramps or pain can stem from many factors—what you eat, when you eat, how you hydrate, the intensity of your runs, and even your breathing patterns.
The key is to identify the most likely cause of your symptoms so you can make targeted adjustments to your nutrition, hydration, and training strategies. With the right tweaks, most runners can significantly reduce or even eliminate stomach issues on the run.
However, if your symptoms persist despite trying these approaches, it’s important to consult a healthcare professional. Conditions such as acid reflux, irritable bowel syndrome, or other underlying digestive concerns may be contributing, and getting the right diagnosis will ensure you can run comfortably and confidently.
For a list of great pre-run snacks for your workouts or on race day, check out this next guide:
