You’re finishing up your run and all of the sudden, your belly starts to revolt. It might be cramps, diarrhea, or just an uncomfortable sensation. But what’s to cause this stomach pain after running?
Some of the top causes are changes in gut function during exercise, poor pre-workout meal choices, fueling issues during exercise, recovery meal choices, exercise anxiety, or – more rarely – a severe medical issue. Note that there is more research on stomach pain during running than after running, so some of these are inferences based on that data.
Luckily, as a dietitian and running coach, I think many of these are simple to troubleshoot. Let’s dig into each and how you can prevent the issue from happening again.
Disclaimer: This post was written by Chrissy Carroll, MPH, RD, RRCA Running Coach, USAT Level I Triathlon Coach. It is for informational purposes only and should not be construed as individual nutrition advice. Consult a doctor or dietitian for individualized nutrition advice.
1. Changes in blood flow to the gut
When you exercise, the body must shift some blood flow away from the gastrointestinal tract and to your workout muscles. This allows the muscles to get the oxygen and fuel they need to continue working out.
The downside, of course, is that the decreased blood flow to the gut can cause stomach upset.
Research shows that the longer and more intense the exercise is, the greater the reduction in blood flow to the gastrointestinal system. In fact, with long duration and intensity, normal blood flow to that system may be decreased by 80 percent or more! This is why many folks may end up with stomach upset towards the end of their run.
While you can’t necessarily change the biology of your body, there are certain factors that research shows may reduce the risk of GI symptoms associated with this reduced blood flow. These include:
- Staying hydrated on your run, as dehydration can contribute to stomach issues. Newer research showed a link between being less hydrated and experiencing more GI symptoms 24 hours after a marathon.
- Reducing the intensity of exercise slightly, as this can preserve more blood flow to the gastrointestinal system (the feasibility of this may of course depend on your training goals and plan, though). If you’re newer to running, work slowly to build your running base before adding in too much intensity.
- Avoiding NSAIDs (like ibuprofen) before or during a run, especially in the heat.
2. Intestinal cell injury
Exercise of prolonged duration, especially at a high intensity, can cause damage to the intestinal cells. This causes increased intestinal permeability – in other words, things slip through the intestinal tract that shouldn’t be slipping through. Biomarkers of intestinal permeability remain elevated for a while after running, which may explain the increase gastrointestinal symptoms after a race or training run.
Like changes in blood flow, you can’t necessarily change your body’s response to exercise. But there are strategies you might consider to limit this response:
- Reduce eccentric load – i.e. downhill running – on your training runs, if feasible for your training plan and goals. Research from 2023 notes: “More eccentric load and having to work harder to maintain a pace/goal time creates greater metabolic heat and, thus, for that individual nearing their threshold, greater GI damage.”
- Reduce intensity, if feasible for your training plan and goals, as noted above.
- Acclimate to hotter temperatures during training and/or racing, which may help reduce intestinal injury during a run. If your race will not be in hotter temperatures but you live in a warm climate, consider doing your training runs in early morning or early evening when the temperatures are cooler.
- Try compression socks – one small study found that wearing compression socks limited markers of intestinal damage after a marathon.
3. Eating your pre-workout meal too close to your run
Pre-workout meals are great for providing your body with the fuel for supporting your upcoming workout. However, eating your meal too close to your run can cause stomach upset during or towards the end of your run. This is largely related to the changes in blood flow noted above, and the fact that your body may not have had enough time to process what you ate.
Generally, pre-workout meals should be eaten 1-4 hours before a run. If you’re eating several hours before, you have flexibility for a larger meal with more diverse components. If you’re eating an hour before, you generally want to stick to a smaller meal that has easily digestible carbohydrates.
4. Too much fat and fiber in your pre-workout meal
Fiber and fat can both slow digestion, which can cause GI upset on a run. The closer to your run that you eat, the more important it is to minimize fat and fiber (if you find they cause issues for you). This might look like switching from a higher fiber cereal to a lower fiber cereal, or skipping the bacon that you usually add to your breakfast sandwich.
5. Combining fuels during exercise
One of the most common causes of stomach pain at the end of a run? Combining fuel products at the same time while running.
For example, let’s say you really like using energy gels and sports drinks on your long run. That’s totally fine, but you want to stagger them. If you take a gel and then gulp a bunch of sports drink at the same time, that’s creating more concentrated solution of carbs in the stomach that can be difficult to digest at once.
The impact on the gut can add up over time on your run, often leading to issues towards the middle to end of the workout.
Instead, try having the gel with water or an electrolyte drink, and then a little while later chugging your sports drink. This gives the stomach time to process the fuel.
6. Overconcentrating your sports drink
If you’re using a powdered sports drink, more does not always equal better. Sometimes folks will double up the powder to get more carbs in a smaller volume of fluid. But like what was described above, this can create a solution that’s too concentrated and causes gastrointestinal upset over the course of a run.
Instead, follow the manufacturer’s directions for the optimal solution concentration.
7. Only using fuel on race day
You know how you need to train your body to run for long distances? You also have to train your gut to be able to handle fuel on those distances!
If you only ever use fuel on race days, it’s likely that you may experience stomach upset after your run because your body wasn’t used to processing fuel at the same time as your run.
This can be avoided by practicing your fuel choices during training runs, finding what works for you, and sticking with that plan on race day.
8. Post-workout recovery food choices
If most of your stomach pain strikes when you eat right after a workout, it could be related to the types of foods you’re consuming. For example, eating a very large or high fat meal when your stomach is still on edge from a long run might cause some cramping or discomfort.
Instead, you could try easily digestible foods that are rich in carbs and protein, and lower in fat. Sometimes liquids are easier on the gut than solid foods, so a glass of chocolate milk or a smoothie might be good options to try right after a long run.
If you find that eating right after a run causes stomach upset, but waiting an hour or so doesn’t – it’s likely fine to just wait it out. Most of the newer research on recovery nutrition suggests there is much more flexibility in nutrition timing than we originally thought. Your everyday diet will likely fulfill your recovery needs, so long as you’re getting enough nutrients over the course of the day and you’re not doing two-a-day workouts. (For competitive athletes doing two-a-days, recovery timing does become much more important right after a workout.)
However, try to make sure you’re rehydrating immediately after your run with slow sips of fluid.
9. Exercise anxiety
The mental side of sport can play just as big of a role in training and performance as the physical side. If you arrive at every long training session or race feeling anxious, that can translate to stomach pain.
This is especially true if the anxiety is related to the fear of gastrointestinal upset, which can then become a self-perpetuating cycle.
If you find yourself worried throughout your run that you’re going to have stomach pain after it’s done, try using one of these techniques:
- Repeat a mantra during the tough parts of your run – my favorite is “Calm your breathing, you are fine”. This may help regulate your response to the intensity of the run.
- Try box breathing when you finish your run. Breathe in for 4 counts, hold at the top for 4 counts, breathe out for 4 counts, and hold at the bottom for 4 counts.
- During your run, visualize yourself feeling calm and healthy after you finish.
- Meditate when you finish your run.
Yes, it sounds a bit woo, but some research has found a link between anxiety and gastrointestinal symptoms in long-distance running – so worth a try.
10. Additional Tips to Try
In addition to these common causes, there are some other tips that I found in the research or anecdotally with clients:
- Wear leggings that aren’t compressing your belly. Sometimes tight high waisted leggings can press against your stomach and cause issues.
- Try a low FODMAP diet if the previous nutrition information didn’t help. One study found that a low FODMAP diet reduced gastrointestinal symptoms in runners. Symptoms were measured during exercise, but could help afterwards too.
- Consider a probiotic supplement, as a study on marathon runners and another study on runners in the heat both found positive impacts of probiotics on reducing GI symptoms. These symptoms were during exercise but may be worth trying for stomach upset after exercise too.
11. Rule out severe medical issues
Many years ago, I met someone that was having a ton of stomach pain during and after her runs. As it turned out, her issue was caused by a severe gastrointestinal disorder that was discovered during an evaluation by her doctor. If you’re running and constantly getting severe stomach pain during and after your workout, regardless of tweaks to your nutrition plan, it’s worth getting checked out by a doctor.
The Bottom Line
If your stomach is hurting after running, try adjusting your pre- and during-workout nutrition plan. You can also try reducing your levels of exercise anxiety, or reducing the intensity of your runs. If none of these are effective, or you’re experiencing severe pain, be sure to see a doctor to rule out any medical conditions.
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