Many runners know the feeling: Your legs feel strong, your fitness is there, but your stomach can act up during the run. Diarrhea, cramps, or sudden urgency can affect both training and racing, even when everything else is on point.
The good news is that you can often do a lot yourself. By adjusting diet, timing, fluids, and your choice of sports nutrition, many people can reduce the risk of stomach issues. Here’s a guide you can try in your own training and use to fine-tune your energy and gut strategy.
What is runner’s stomach and why does it happen
“Runner’s stomach” is used as an umbrella term for gastrointestinal discomfort during or after running. It can range from mild discomfort to symptoms that make you slow down or stop along the way.
Typical symptoms can include:
- Sudden urge to have a bowel movement or diarrhea
- Cramps or a dull ache in the stomach
- Gas and bloating
- Nausea or general discomfort
Often, several mechanisms are at play at the same time:
- Blood redistribution when you run, blood is prioritized to the muscles rather than the gut, which can challenge digestion, especially if the stomach is very full
- Mechanical impact each step can affect the gastrointestinal system, and the harder and longer you run, the greater the strain you may experience
- Diet and fluids large, heavy meals close to the start, lots of fat, fiber, protein, or large amounts of sugar and sweeteners can be hard to handle when your heart rate is high
- Energy and drinking strategy lots of carbohydrates at once, very concentrated drink, or conversely too little fluid can cause unsettled stomach for some
It’s rarely a single product that is the cause. Often, it’s about the combination of amount, timing, and composition—and that’s exactly where you can adjust and test your way forward.
Eat your way to a calmer stomach before running
What you do in the hours leading up to a run can affect how your stomach feels at the start. A simple rule of thumb is to give digestion time.
Many runners find that the following works well:
- Last larger meal about 2 to 3 hours before running
- Smaller snack 60 to 90 minutes before, if you know your stomach does well with it
Close to running, many choose to cut back on:
- A lot of fat such as fried foods, fatty cheese, cream, or large amounts of nuts
- High fiber content from lots of whole grains, vegetables, and legumes
- Large amounts of protein from heavy meat dishes or very high-protein meals
- Highly spicy food and alcohol
Instead, you can focus on relatively easy-to-digest carbohydrates, for example:
- White bread with a thin layer of topping
- White pasta or rice with a little mild topping
- Banana or other ripe, soft fruit
- Sports products you’ve tested before, such as a gel or a little sports drink
Some runners experience a calmer stomach if they eat a bit lower-fiber for one to two days leading up to an important race. It may be relevant to test over a period and note how your stomach responds, so you can find your own routine.
Carbohydrates without chaos during running
Carbohydrates during running can help maintain energy levels on longer runs. If you exceed your stomach’s comfort zone, however, it can cause unsettled feelings. That’s why it’s often about finding a level where both energy intake and your stomach work in practice for you.
For many runners, it makes sense to aim for:
- About 30 to 60 grams of carbohydrate per hour on runs around 60 to 120 minutes
- Up to 60 to 90 grams per hour for longer and/or harder efforts, provided the stomach is accustomed to it
How much that is in practice depends on your products. One Energy Gel often contains around 20 to 30 grams of carbohydrate. As a rule of thumb, you can for example:
- Take about one gel every 30 to 40 minutes if you’re aiming for 30 to 60 grams of carbohydrate per hour
- Supplement with sports drink or chews if you want to get closer to the higher ranges
You can see the carbohydrate content of the individual variants in PurePower’s energy gels for running and use it to fine-tune your plan.
Two principles often make a difference for the stomach:
- Start low and build up stay at the low end of the range and increase slowly over several weeks, so you can gradually get your gastrointestinal system used to energy intake while moving
- Distribute the energy evenly instead of taking two gels at once after an hour, you can split it into smaller doses throughout the hour, which often feels gentler and can provide more stable energy
Gels and chews for a sensitive stomach
Many people worry whether it’s the gel itself that causes stomach problems. In practice, it’s often more about the total amount of carbohydrates, the concentration, and fluid intake than the format itself.
Gels can be a practical solution when:
- You’re running at a high pace and want carbohydrates that are easy to consume on the go
- You want a more precise carbohydrate intake at specific times, for example at aid stations
- You want as little chewing as possible when intensity is high
You can dive deeper into dosing and stomach tolerance in the article Can you take too many gels?.
Chews can be a good alternative for a sensitive stomach because:
- You can eat small bites continuously instead of one whole shot of energy at once
- Some find it easier on the stomach when carbohydrates are consumed in smaller portions
- It can feel more like regular food, which can be nice on long runs
If you want to test that strategy, you can look at PurePower’s energy chews as gentle energy and try them on your long training runs well ahead of an important competition.
For many, a combination works well, where chews can be used for ongoing intake and a gel can be used as an extra supplement—for example before a hill or toward the end of the race—if it fits your plan and your stomach.
Fluids and electrolytes for a calmer stomach
Fluids are important, but too much, too little, and overly concentrated intake can all cause stomach upset. It can therefore be relevant to find a routine that suits both the workload and comfort.
Pay particular attention to:
- Your general hydration status during the day it is often more appropriate than drinking a lot right before the start
- Intake during running small, regular sips rather than drinking large amounts infrequently
- Combination with gels when you take a gel, drinking water with it can work for some so the mix doesn’t become too concentrated
- Combining products avoid, if possible, combining very sweet sports drink with many gels at once if you know your stomach is sensitive
In hot conditions, long sessions, and with a high sweat rate, you also lose electrolytes through sweat. Here, electrolyte tablets in your bottle can be a simple option that can help maintain fluid balance as part of an appropriate hydration strategy. For example, you can test PurePower’s electrolytes on your longer runs.
Train your stomach like you train your legs
The gastrointestinal system can, like muscles, adapt to the stress you expose it to. However, it may require that you work gradually and give your body time to get used to both distance and energy intake.
This can mean, among other things, that you:
- Build up distance gradually, especially if you already tend to have stomach problems
- Practice taking in energy and fluids in training in the same way you will do on race day
- Change only one thing at a time, for example a new product, a new amount, or new timing
That way, you can better see what works for you and what doesn’t. A simple log can be a useful tool. For example, note:
- What you ate, and when you ate it
- What and how much you drank before and during the run
- Which products you used along the way
- Length and intensity of the session
- Which stomach symptoms occurred, and when they appeared
After a few weeks, you will often be able to spot patterns and typical triggers that you can adjust and actively use in your planning.
Race day without unnecessary stomach upset
As you approach an important competition, it can help your stomach if there are no surprises. The goal is for the key choices to have been tested in advance, so you know what works for you.
This can for example mean that you:
- Stick to the products and amounts you have tested in training, with no new experiments on the day
- Plan your last larger meal about three hours before the start with easy-to-digest carbohydrates, moderate size, and limited fat and fiber
- Use a small snack, such as half a piece of white bread, a banana, or a small gel 60 to 90 minutes before, if you know you tolerate it
- Have a fixed toilet routine many find that a cup of coffee at home, if their stomach does well with it, combined with plenty of time in the bathroom, can create more calm
- Follow your tested energy and hydration strategy at regular intervals during the race instead of doing things spontaneously
If you want more concrete numbers on carbohydrates and fluids per hour for your specific distance, PurePower’s Fuel Guides can give you a good starting point, which you can then adapt to your own stomach and your training.
There is no one universal solution to runner’s stomach. But by working systematically with pre-run diet, carbohydrate dosing, fluids and electrolytes, and gradual habituation, many runners can reduce stomach issues and have better experiences both in training and on race day. If your symptoms are severe, change significantly, or persist, it’s a good idea to get an individual assessment from a doctor or other healthcare professional.