If you’ve ever hit the wall during a long run, you know how brutal it feels. It happened to me during my first marathon, and running the last 10k was beyond brutal.
Your legs are heavy, your energy crashes, and suddenly the miles ahead feel impossible. Most runners assume it’s a training issue, but more often than not, it’s a fueling problem.
In this post, I’m breaking down exactly how to fuel a marathon (and long runs in general) with insights from registered dietitian and ultramarathoner Amy Goblirsch. From carbs per hour to gels vs. real food, here’s what you actually need to know to run strong from start to finish.
Why Most Runners Underfuel
One of the biggest mistakes runners make is simply not eating enough during their runs.
Even experienced runners fall into this trap. As Amy shared:
“I look back at my first marathon where I made all the mistakes I tell runners not to make… I didn’t carb load, I took half a gel at mile 15… I didn’t eat post-run… every single mistake.”
The result? Poor performance, slow recovery, and that dreaded crash late in the race. Most runners think they don’t need sugary gels to perform, or they think sports products are “bad” for them. But, in actuality, your body needs fuel after the first hour of exercise.
Glycogen stores run out after about 60 minutes, and your body is running on empty. This severly impacts performance and makes you feel terrible, especially during a multi-hour race, like the marathon. You can’t rely on willpower to get through a marathon. You need fuel.
How Many Carbs Do You Need Per Hour?
When it comes to fueling during a run, carbs are king. Amy recommends focusing less on total calories and more on carbohydrate intake. “If you’re going to be running over two and a half hours… that would be aiming for 60 to 90 grams of carbs per hour,” says Goblirsch.
That might sound like a lot, but newer research (and what elite runners are doing) is pushing those numbers even higher.
Why? Because carbs are your body’s preferred energy source during endurance exercise. If you don’t replenish them, you’ll eventually run out—aka, hit the wall.
However, you can’t push to the upper limit of the carb range without training the gut to tolerate that amount. Start small (15-30g/hour) during training runs and work your way up to something more significant).
When Should You Start Fueling?
Here’s where most runners go wrong: they wait too long to start fueling during the race.
“You want to fuel from the first 30-minute mark,” says Goblirsh. “You don’t want to wait too long to fuel and dig yourself into a hole. It’s going to be so hard to dig yourself out of that.”
You need to take in a lot of fuel during a marathon, so it’s best to start early in order to get enough. Even if your run is under 2 hours, practicing early fueling helps you:
- Train your gut
- Build a race-day strategy
- Avoid late-run energy crashes
Bottom line: Don’t wait until you feel tired. Fuel before you need it.
Gels vs. Chews vs. Real Food
There’s no one-size-fits-all approach to fueling—it’s about what works for you. “That can be from gels, chews… or food sources like a banana, a granola bar… and endurance drinks like Gatorade… all of that can help you meet those carb needs,” says Goblirsch.
Not a fan of gels? You’ve got other options, like :
- Gummies or chews
- Sports drinks
- Candy (yes, really)
- Real food like bananas or bars
Sports drinks, gummies and chews are formulated to be tolerable for runners during a race, meaning they shouldn’t cause too much GI distress. But other options work too. Find out what works best for you during training.
Can You Train Your Gut? (Yes—And You Should)
If you’re thinking, There’s no way my stomach can handle that much fuel, you’re not alone.
But gut training is real, and it works. “Training your gut is a thing… it’s not just about training your legs… it’s also training your stomach to figure out the fuel that works best for you,” says Goblirsch.
Start small and build up:
- Begin with lower carb intake per hour, like 15-30 grams, then build to 30-60 grams and so on
- Gradually increase during training runs
- Test different fuel types and timing
This is how you avoid race-day GI issues and actually absorb the fuel you’re taking in.
Hydration Matters More Than You Think
Fueling isn’t just about food. Hydration plays a huge role in performance and digestion. “Dehydration can not only decrease performance, it can lead to GI issues. So it’s very important to stay hydrated,” says Goblirsh.
As an added bonus, sports drinks can help you hit your carb goals, too.
For example:
- A gel = ~20–40g carbs
- A sports drink = ~20g carbs
Combine them, and you’re much closer to your hourly carb target without needing extra fuel.
The Mistake That Leads to Injury and Burnout
Fueling doesn’t stop when your run ends. In fact, one of the biggest issues Goblirsch sees is runners not eating enough after long runs: “You can’t only listen to your hunger cues… your hunger cues will not lead to supporting recovery.”
After long runs, appetite often disappears, but your body still needs carbs to replace glycogen stores and protein to help with muscle repair.
If you’re feeling depleted after a long run, try these recovery strategies:
- Drink your calories (smoothies, chocolate milk)
- Set reminders to eat
- Add calorie-dense foods like avocado
Failing to refuel properly can lead to poor recovery, which may increase your risk of injury and make tomorrow’s workout feel harder.
Do Slower Runners Need Less Fuel?
The short answer is no. “They still need to be within that 60 to 90 grams of carbs per hour,” affirms Goblirsch.
In fact, slower runners may need more total fuel because they’re out on the course longer. This is why fueling strategies should be based on time, not pace.
The Bottom Line: Fueling Is a Performance Tool
For years, carbs and sugar have been misunderstood—but in endurance sports, they’re essential.
As Amy put it: “It’s really about using what works best for you… and understanding that sugar is what your body needs to perform.”
When you fuel properly, everything changes. You feel stronger mid-run. You finish faster. You recover better.
And most importantly—you actually enjoy the run.
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