Why Do I Get Nauseous During Long Runs? 7 Causes Runners Should Consider
The half-marathon portion of my half-ironman was an out and back loop, so you could see the athletes that were miles behind you or ahead of you. I was passing mile 8 when I saw a guy bend over and vomit at his mile 4. At this point in a 70.3 race we've already swam over a mile, ran between transitions, and biked 56 miles. It's already been a long day and we've got this half-marathon to run. So, this guy getting sick at mile 4 isn't uncommon.
In fact, you may be at mile 7, 10 or maybe even 15 when your stomach starts to turn. Your legs feel fine and you're barely winded, but your stomach has decided to make you feel sick.
Suddenly, you're nauseous and the thought of taking another gel makes you want to throw up. Ugh, I've so been there and it sucks.
You might be thinking, what tha' heck?!
If you experience nausea during long runs, half marathons, marathons, or ultras, you're definitely not the only runner dealing with this.
But here's what I want you to know:
Nausea isn't always just a fueling problem.
Your gel may be involved, but there can be several pieces to the puzzle.
1. Blood Is Moving Away From Your Gut
When you're running, your body has priorities.
Muslces, heart, and temperature regulation.
Your body is exerting harder work on your muscles making your heart work harder and more blood to be redirected to your muslces to keep them working optimally. Your body is heating up and has to work to keep you cool.
What does this mean for digestion?
Not exactly priority #1.
As exercise becomes longer or more intense, blood flow to the digestive system can decrease. For some runners, this can contribute to nausea, cramping, diarrhea, or that awful sloshy-stomach feeling.
2. You're Running Too Hard
Ever notice that your stomach is fine during an easy run but falls apart during a race?
Intensity matters.
The harder your body is working, the greater the demand on your entire system. Basically what we just described above, but magnified.
That's one reason your nutrition strategy needs to be practiced under conditions that actually resemble race day.
3. You're Dehydrated
Your gut needs adequate blood flow to function and your blood is a liquid substance that needs water and electrolytes.
Dehydration combined with prolonged exercise can create a difficult environment for digestion. That being said, more "water" doesn't always mean better. In fact, you might find drinking straight up water makes your nausea worse.
Your hydration strategy should account for your sweat rate, weather, duration, electrolytes, and what you're actually able to tolerate. This is where testing your hydration strategy is key during training.
4. You're Asking Your Gut to Handle Too Much Fuel
Maybe you're taking a gel every 20–30 minutes because that's what your training buddy does, but can your gut tolerate it?
Large amounts of carbohydrate that aren't well tolerated or absorbed can contribute to GI symptoms. This doesn't necessarily mean carbohydrates or gels are bad. It may mean your strategy needs work.
5. You Haven't Trained Your Gut
We train our legs, pace, hills, and even heat/cold tolerance; but are you training your gut?
For some, its not until race day that their digestive system gets a challenge to process hours worth of carbohydrates and fluids while running. They hear "carb load" and get after it with pasta the night before and heavy fiberous foods the morning before, but have never actually tested these foods out. This can be detrimental to the race day experience.
Your gut needs training, too.
Long runs are your opportunity to practice your fueling and hydration strategy. It gives you an opportunity to practice and learn what your body can tolerate.
6. Heat May Be Making Things Worse
Hot race? That's another variable.
Your body is simultaneously trying to cool itself, maintain performance, hydrate, and digest whatever you're putting into your stomach.
If nausea seems worse during hot training sessions or races, pay attention to that pattern.
7. It May Not Be Just Your Gel
This is the big one.
When runners experience nausea, diarrhea, bloating, or cramping, they often immediately blame the gel and change brands.
Then change again.
Then eliminate food.
Then try running fasted.
But what if the gel isn't the entire problem?
I want to know:
What did you eat before the run?
How much carbohydrate are you consuming?
How much are you drinking?
When do symptoms start?
Does intensity change them?
Do you have digestive symptoms when you're not running?
Does this happen every long run or only under certain conditions?
That's how we start identifying a pattern instead of randomly removing foods and changing products.
Stop Guessing. Start Investigating.
If your stomach occasionally feels off during a hard run, that doesn't necessarily mean something is wrong.
But if nausea, vomiting, diarrhea, bloating, or stomach cramps repeatedly interfere with your long runs or races?
Pay attention.
Your gut is giving you information.
Your race-day gut strategy doesn't start the night before your marathon.
It starts during training.
The goal isn't simply to survive race day without throwing up, but instead, to stand at that starting line confident that you've trained your gut along with the rest of your body.
Ready to figure out what's triggering your runner's gut?
Start with my free Runner's Gut Decoded Self-Assessment to identify patterns that may be contributing to your symptoms.
Dr. Lexi Lain
Naturopathic Doctor | 4x Half-Ironman Finisher | Fix Runner's Gut
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