Nausea in the middle of a marathon can feel like hitting a wall, both physically and mentally. For some it creeps up, for others it strikes suddenly with a heavy stomach, dizziness, and the urge to slow down or stop.
Below you’ll get a concrete, down-to-earth walkthrough of why nausea during a marathon is common, what typically lies behind it, and how you can plan training, energy, and fluids so you can reduce the risk the next time you’re on the starting line.
What happens in the body during a marathon?
During a marathon, the body is working at full throttle to keep you moving. That means, among other things:
- More blood to muscles and skin to get rid of heat
- Less blood to the digestive system
- Higher heart rate, faster breathing, and more stress hormones circulating
This combination can make the gastrointestinal system more sensitive. At the same time, you often expose it to:
- Carbohydrates in larger amounts than in everyday life from gels, chews, and sports drink
- Fluids in irregular amounts
- Heat and a high sweat rate
- A race pace that is at or above your normal training pace
For some, this can cause nausea, a heavy feeling in the stomach, reflux, belching, or vomiting. It’s often not due to one single factor, but a combination of energy, fluids, heat, pace, and preparation.
If you want to dive deeper into the link between energy, fluids, and performance, you can find inspiration in the Energy collection.
Typical causes of nausea during a marathon
The causes of nausea can vary from runner to runner, but certain patterns show up for many marathon runners.
Too much energy in too short a time
A classic cause is that energy intake becomes too concentrated for the stomach. Many experience discomfort when they:
- Take several gels right after one another
- Skip water when taking gels
- Go from very little energy in training to a very ambitious plan on race day itself
This can create a high concentration of carbohydrate in the stomach, which not all stomachs tolerate well—especially when blood flow to the gut is already reduced during running.
Imbalance in fluid intake
Both too little and too much fluid can help trigger nausea.
With too little fluid, some may experience:
- Headache
- Dizziness
- Nausea and a feeling of overheating
With very high fluid intake, the body may conversely have a harder time maintaining balance between fluids and salts. For some, this shows up as nausea and general discomfort. More fluid is therefore not automatically better; it’s about a plan that fits you and the conditions on the day.
The food you eat before the start
What you eat before the race can have a big impact on your stomach during the run. Large, fatty, or very high-fiber meals close to the start can sit in the stomach for a long time and, during running, increase the risk of:
- Nausea
- Side stitch / pain in the side of the abdomen
- Reflux and heartburn
For many, a more easily digestible meal three to four hours before the start works better, often with a focus on carbohydrates and limited amounts of fat and fiber.
Heat and high humidity
On hot and humid race days, the body uses extra resources to regulate temperature. You sweat more, lose more electrolytes, and are challenged faster on fluid balance. For some runners, nausea can be a sign that the heat load is getting too high and that pace and the fluid plan may need adjustment.
Too hard a pace relative to training
If you’re running faster than the pace you’ve trained at on your long runs, both heart rate and overall strain increase. That extra intensity can be enough for the stomach to react, even if energy and fluids look appropriate on paper. Here it can help to match the pace to the level your body and stomach are used to from training.
How to train your stomach for race day
Nausea isn’t only about what you do on race day itself. To a large extent, it’s also about what you’ve accustomed your body to in day-to-day training.
Gut training means that you deliberately train your stomach to:
- Absorb fluids while running
- Handle carbohydrates from gels, chews, and sports drink
- Function at the pace you plan to race at
You can do this, among other ways, by:
- Using your long runs from about 60 to 90 minutes and up to mimic your race plan
- Starting with a lower carbohydrate amount per hour and gradually building up
- Noting timing, product, and reaction so you can spot patterns in what calms or upsets your stomach
- Testing both gels, chews, and sports drink in advance—not for the first time on the day
If you want to see what a complete energy and fluid plan before, during, and after a marathon can look like, you can start with Energy Gel - Sample Mix and adjust to your stomach and your level.
Carbohydrates without nausea
Nutrition recommendations for endurance sports often suggest that many runners can aim for roughly 60 to 90 grams of carbohydrate per hour during a marathon—if the stomach is trained for it. However, it’s a guideline range, not a requirement.
A practical way to think about dosing is:
- First gel after about 30 to 45 minutes
- Then steady intake, for example every 20 to 30 minutes
- Always with a little water at the next aid station or from your own bottle
A typical challenge is taking several gels close together out of fear of running out of energy. That can cause a heavy, nauseous stomach—especially if they’re taken without water. In practice, for some it can be an advantage to:
- Distribute the energy in smaller bites, for example with chews
- Alternate between gels and energy drink, so the stomach isn’t only getting a very concentrated gel
If you want to nerd out more about the relationship between dosing, the stomach, and nausea, you can read the guide can you take too many gels? nausea and dosing.
Fluids and electrolytes in your plan
Nausea is often linked to how you manage both fluids and electrolytes—not only how many carbohydrates you get.
With too little fluid, you may experience, among other things:
- Increased heart rate and higher perceived exertion
- Headache, dizziness, and nausea in some runners
- The body having a harder time getting rid of heat
With very high fluid intake, on the other hand, you may experience:
- Sloshing stomach and nausea
- Discomfort when leaving the aid station because your stomach feels too full
For many, it works better to:
- Drink small sips evenly distributed between aid stations
- Adjust the fluid amount based on heat, sweat rate, and intensity
- Get both fluids and carbohydrate from a sports drink with electrolytes instead of only water
Here a carbohydrate and electrolyte solution like Carbo Race Electrolyte Elderflower 1kg can be part of your plan, because it provides carbohydrates and electrolytes that can support fluid intake during longer sessions.
Choosing a format that suits your stomach
There isn’t one energy format that fits everyone. It’s about finding the combination your body typically tolerates best.
- Gels deliver a high concentration of carbohydrate at once, often require water for many, and are practical when you want compact energy
- Chews can be spread out over longer time, so you control energy in smaller bites, and many find them gentler
- Sports drink combines fluids, carbohydrate, and electrolytes and suits runners who want to drink part of their energy
A solution for many is a strategy where you combine multiple formats. For example, you can:
- Start calmly with sports drink in the first kilometers
- Use gels when the pace increases or when you start to get tired
- Supplement with chews if you want to spread the energy out more and reduce the risk of stomach upset
If you want to test what your stomach tolerates best, a pack like mix of gels and chews to test your stomach can make it easier to try different combinations of flavors and formats.
For race day itself, an all-in-one solution like Marathon Mix Pack ready race day pack can make it easier to have gels, chews, snacks, electrolytes, and a soft flask all together so you can focus on the race and your plan.
What you can do if nausea hits
Even with a well-thought-out plan, nausea can occur. Here’s a simple approach you can use mid-race.
- Dial the pace down slightly for two to five minutes to reduce the strain
- Breathe calmly and deeply and avoid hyperventilating
- Take a short break from energy; for example skip one planned gel or chew, but continue with small sips of water
- Switch to a milder format, such as small sips of sports drink or a few chews instead of a whole gel
- Shift focus to letting your stomach settle instead of chasing seconds on the next kilometer
You should consider stopping and seeking help if nausea is accompanied by:
- Severe dizziness or confusion
- Chest pain or severe headache
- Very strong sensation of heat or chills
- Persistent vomiting and inability to keep fluids down
In those situations, it’s often more important to prioritize safety and listen to your body than to stick to a specific time.
Short FAQ about nausea and marathon
- Is nausea during running normal? Yes, it’s relatively common among marathon runners, especially at high intensity, in heat, or if the energy and fluid plan hasn’t been tested in training.
- Can both too little and too much fluid cause nausea? Yes, low fluid intake can cause nausea in some, and very high fluid intake can also disrupt the balance between fluids and salts and cause discomfort.
- Does the food before the race matter? Yes, large, fatty, heavily spiced, or very high-fiber meals close to the start can increase the risk of stomach issues and nausea.
- Can sports drink help? Sports drink can contribute both carbohydrate and fluids, but the amount and concentration should suit you and be tested in training.
- Is nausea always a sign that I should stop? Not necessarily. Mild to moderate nausea can in some cases subside if you adjust pace, fluids, and energy. However, accompanying symptoms like dizziness, confusion, pronounced heat stress, or repeated vomiting should be taken seriously.
Nausea during a marathon is rarely random. Often, it’s a signal from the body that load, energy, fluids, and heat aren’t fully working together. With a well-thought-out plan, targeted gut training in everyday training, and realistic expectations for pace, many runners can reduce the risk and have a more stable experience all the way to the finish line.