How to Prevent Runner’s Stomach from Ruining Your Next Long Run or Race

After crossing the finish line of the Boston Marathon earlier this year, I only made it a few steps before I bent over and threw up three times in a row. This wasn’t surprising. 

I’d been nauseated for the past 10 miles, and made two porta-potty stops and multiple visits to medical tents to beg for sodium. I couldn’t figure out whether my runner’s stomach symptoms were thanks to drinking too much water or too little. But by the final two miles, I stopped questioning, sipping my water bottle, or trying to control the queasiness, and just gave everything my legs had left in them until I hit mile 26.2. Then I let it all come up. 

I’m sure I wasn’t the only one whose gut rebelled that day. Runner’s stomach is an annoyingly common side effect of putting in long, hard miles. Research estimates that about 30–50 percent of endurance athletes experience gastrointestinal (GI) symptoms at some point during intense exercise. 

Although there are usually no long-term medical risks to running so fast that your stomach yells “uncle,” it can certainly feel unpleasant in the moment, and it’s a quick way to ruin an otherwise good run. Here’s what you need to know so your gut doesn’t get in the way of setting new PRs.

What Is Runner’s Stomach?

Sometimes called “runner’s gut” or “runner’s belly,” runner’s stomach involves a “constellation of symptoms,” according to Wendi LeBrett, MD, a gastroenterologist in California. “It can be a little bit different for every runner,” she says. While some of us may get diarrhea (unaffectionately known as “runner’s trots”), others might have abdominal pain, cramping, side stitches, and bloating. “Typically, they tend to be lower gastrointestinal symptoms, but some people report upper gastrointestinal symptoms too, like pain higher up in the stomach and heartburn,” she says. 

The condition can even show up differently in the same runner from day to day: On one run it might just be some annoying bloating, but on another the symptoms might require an urgent search for the nearest toilet ASAP. 

Common Causes of Runner’s Stomach

Just like there are a number of different factors that can help you become a faster runner, there are also several things that can lead the GI tract to launch a revolt.

1. There’s Decreased Blood Flow to the Gut

On a tough run, your muscles require more blood than usual to get the oxygen they need to keep contracting and propelling you forward. Dr. LeBrett says that can mean your gut ends up with less of the blood that it needs to function normally, leaving you with an upset digestive system. 

2. You’re Triggering a Fight-or-Flight Response

If runner’s stomach symptoms sound similar to how your body reacts when you’re stressed, that’s because our sympathetic nervous system doesn’t distinguish between physical and emotional stress. Furthermore, while the sympathetic fight-or-flight response evolved as a survival mechanism designed to keep you safe from harm, your nervous system has trouble differentiating between what’s actually dangerous and what’s not—meaning it can go into overdrive if it mistakes your tempo run for the need to escape a lion. “When that happens, it’s easier to get rid of your gastrointestinal waste to make you lighter and faster,” Dr. LeBrett says. 

This can be exacerbated on race day, or any run when nerves get involved, adds Danielle Crumble Smith, RD, a dietitian who specializes in working with athletes. Put together, the physical and mental stress add up to gut issues you’d never see during an easy jog. “A lot of people, myself included, before a track meet, it’s like, ‘Oh, I've got to go to the bathroom,’” she says. “And for other people, stress translates to constipation. It can go either way.” 

3. Your Intestines Are Getting Bounced Around 

The up and down motion of running—and the hard impact when you hit the ground—can do a number on your intestines. “As we are running, we’re jostling our body, and that can contribute to peristalsis [wave-like contractions] moving through our digestive tract very quickly. And then suddenly, we’ve got to use the bathroom,” Crumble Smith says.

4. You’re Waterlogged 

Before racing long distances, runners are told to carb load so they can fill their muscles with fuel to stave off fatigue. But sometimes that can have detrimental side effects. “That big sugar load into the intestines can bring in more water,” Dr. LeBrett says. This can also happen if you guzzle too much water (or coffee) before or while running, Crumble Smith adds. The extra liquid bouncing around in your gut can cause cramping and diarrhea.

5. You’re Dehydrated

On the opposite side of the equation, not having enough water in your system can also cause its own set of issues. “[Dehydration] can contribute to abdominal cramping and GI distress in general,” Crumble Smith says. 

6. You Need More Food

If you haven’t eaten enough before your run, a too-empty stomach can also be a culprit, according to Crumble Smith. This is why she suggests munching on a protein-carb combo before lacing up to sustain you throughout your run (since carbs will give you quick energy and protein will keep you full longer).

How to Treat Runner’s Belly During a Run or Race

When runner’s stomach symptoms hit, Crumble Smith suggests listening to your body’s cues and honoring them as soon as you can. “With some of my runners, they will get the sensation to use the bathroom mid-run and not [go]. As a result, they end up constipated,” she says. By ignoring your needs, you can miss the window, she says, and end up even worse off. “If you try to hold it in and you need to use the bathroom, well, then that’s going to cause increased gas that could cause bloating [or] other discomfort, and that can make a run miserable.”

If you don’t necessarily need a bathroom (or don’t have access to one right away), intentional deep breathing can help in the moment to calm your nervous system and ease it out of fight-or-flight mode. “Whether it’s 4-7-8 breathing, box breathing, just taking a pause and doing that can be helpful,” Crumble Smith says. 

Alternatively, if you think being overly hungry might be behind your symptoms, Crumble Smith suggests eating a little snack that might help settle your stomach. “Even something like a rice cake,” she says.

Most of the time, you can keep running safely as long as you don’t mind pushing through the discomfort. “But I would stop if symptoms continue to worsen during the run,” Dr. LeBrett says, adding that blood in your stool or vomit could indicate you’re not getting enough blood flow to your gut. If you notice these warning signs, or if your symptoms last for more than 24 hours, book some time with a doctor ASAP to discuss what’s going on, Dr. LeBrett recommends. Even if you simply start to notice runner’s stomach issues happening more and more often, it’s a smart idea to chat with your medical provider. They can help to make sure something more serious isn’t going on, and give you some personalized ideas on how you might modify your routine to find a little relief. 

“There are ways to help, even if it doesn’t seem like a very serious problem,” Dr. LeBrett says. You can also consider consulting a registered dietitian to identify trigger foods you might have overlooked.

How Long Does Runner’s Stomach Last?

Symptoms typically ease up soon after you stop running, or once you’ve used the bathroom or thrown up, depending on the exact issues you’re dealing with. But Dr. LeBrett says stomach problems can sometimes last for up to 24 hours, “especially if it’s after a very intense workout, like a particularly long endurance run,” she says. 

On the flip side, some people don’t get runner’s stomach until after their run is over, Dr. LeBrett adds, so don’t be surprised if it only shows up once you start your recovery. 

How to Avoid Runner’s Stomach In the Future

If runner’s stomach has become an all-too-reliable jogging partner for you, there are a few things you can do proactively to help keep symptoms from messing with your miles. 

The Takeaway

Not all runners’ stomachs react the same way to the same triggers—some of us will always be more prone to runner’s belly than others. “Some people’s guts, no matter what they do, they’re [fine],” Dr. LeBrett says. “And for some people, very small changes can upset their stomach.” The key is to figure out what mitigation strategies work best for you, and what you personally need to keep your gut happy. Because when you’re running hard, you don’t need stomach problems making it harder.

This content is for informational and educational purposes only and does not constitute individualized advice. It is not intended to replace professional medical evaluation, diagnosis, or treatment. Seek the advice of your physician for questions you may have regarding your health or a medical condition. If you are having a medical emergency, call your physician or 911 immediately.