There’s nothing quite as frustrating as having your legs feel strong, but your stomach bring your run to a halt.
Whether it’s bloating, cramps, nausea, side stitches, an urgent bathroom stop, or that uncomfortable sloshing feeling in your gut, gastrointestinal distress can quickly turn an enjoyable run into a miserable experience.
The good news? You’re far from alone. Digestive issues are incredibly common among runners, especially during longer runs, hard workouts, and races. In fact, studies suggest that the majority of marathon runners experience some form of gastrointestinal discomfort during training or competition.
This collection of symptoms is often referred to as runner’s stomach or runner’s gut—a broad term for the digestive issues that can occur before, during, or after a run. While the symptoms can vary from runner to runner, the result is usually the same: disrupted training, compromised performance, and a lot less enjoyment on the run.
As a running and nutrition coach, I see runner’s stomach all the time. In many cases, the problem isn’t caused by a weak stomach at all, but rather by a mismatch between a runner’s nutrition, hydration, pacing, and fueling strategy.
The challenge is identifying the specific trigger—or combination of triggers—that is upsetting your digestive system. The good news is that most cases can be significantly improved with a few targeted adjustments.
We’ll explore what runner’s stomach is, why it happens, the most common causes, and evidence-based strategies you can use to prevent digestive distress and run more comfortably and confidently.
What Is Runner’s Stomach?
Runner’s stomach is a loose term that encompasses various gastrointestinal symptoms during running, such as abdominal pain, cramping, nausea, diarrhea, gas, bloating, an upset stomach, the urge 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
Runner’s stomach is rarely caused by one thing—it’s usually a combination of factors working against you at once.
Eating too close to your run is one of the most common triggers.
Food that hasn’t had enough time to digest competes with your muscles for blood flow, and the mechanical jostling of running can turn that into cramping or nausea. Most runners do best leaving at least 2–3 hours after a large meal before heading out.
What you eat matters just as much as when.
Fatty, high-fiber, and protein-heavy meals slow gastric emptying, leaving you feeling weighed down well into your run. Sugary drinks and high-carbohydrate foods consumed immediately before exercise have also been shown to increase the risk of stomach cramps.
Caffeine—common in pre-workout drinks and gels—can further stimulate gut motility and worsen symptoms in sensitive runners.
Blood flow redistribution is an underlying mechanism behind many of these issues.
During intense exercise, your body directs blood toward working muscles and away from the digestive tract. This reduced blood supply to the gut can cause cramping, nausea, and in severe cases, GI distress—particularly at higher intensities.
Hydration habits also play a role.
Both dehydration and drinking too much water too quickly can cause uncomfortable bloating or cramping mid-run. Sipping steadily is generally better tolerated than large gulps.
Running intensity and breathing mechanics round out the picture.
Pushing the pace too hard, especially before your body has adapted, puts extra strain on the diaphragm—the muscle involved in both breathing and core stability.
Uneven or shallow breathing can aggravate this further and is thought to be a contributing factor in exercise-related transient abdominal pain (ETAP), commonly known as a side stitch.
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
Not all foods affect every runner the same way, but some are far more likely to cause bloating and GI distress—especially when consumed close to a run.
Common culprits include high-fiber foods, fatty meals, and foods high in FODMAPs (fermentable carbohydrates that are poorly absorbed in the small intestine), such as onions, garlic, beans, and cauliflower.
Dairy can be a significant trigger for runners with lactose intolerance, even if symptoms aren’t noticeable in everyday life—the physical stress of running can amplify digestive sensitivity.3de Oliveira, E. P. (2017). Runnerʼs diarrhea. Current Opinion in Gastroenterology, 33(1), 41–46. https://doi.org/10.1097/mog.0000000000000322
Less obvious triggers include carbonated drinks, heavily processed or salty snacks, and even chewing gum, which can introduce excess air into the digestive tract and cause uncomfortable bloating mid-run.
Because triggers vary significantly from person to person, a food journal is one of the most practical tools available.
Logging what you eat, when you eat it, and how your stomach responds during runs can reveal patterns that would otherwise be easy to miss. If GI issues are persistent or severe, working with a sports dietitian can help you develop a nutrition plan that supports performance without side effects.
#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 replace a good percentage of your fluid loss by sipping small amounts regularly rather than 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 water4McDermott, 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 to about 6 ounces, 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 shown5Millard-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 evidence6Orrù, 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 carbohydrate concentration 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 while running.
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:
0 Comments