The marathon is a game of energy math: your internal stores aren’t enough for 26.2 miles, so you must learn to refuel mid-flight without stalling your engine.
- Glycogen stores run dry after about 90–120 minutes of running.
- The goal is to consume 30g to 60g of carbohydrates per hour (up to 90g for elite runners).
- Don’t wait for hunger: start fueling early (as soon as 40–50 minutes in or at the 10k mark).
- The golden rule: always take gels with water, never with sports drinks (to avoid stomach distress).
It’s often said that a marathon is run with your legs, your head, and your heart. There’s a fourth element missing, and it’s often the one that decides if you’ll finish with a smile or a struggle: your stomach.
In-race nutrition is, for all intents and purposes, the fourth discipline of marathon training.
You can nail every long run, follow your training plan to the letter, and taper perfectly. But if you blow your fueling strategy, the Mile 20 wall will be waiting for you, as certain as a speed trap on a straightaway. And it’s not because you aren’t fit—it’s because you are biologically “empty.”
Building a gel strategy isn’t rocket science; it just takes a little math and a lot of practice. Here’s the breakdown.
You Trained Your Legs, But Have You Trained Your Gut?
The fundamental concept to grasp is that our body has a limited supply of high-octane fuel (glycogen). For the average runner, this reserve lasts between 90 and 120 minutes of intense effort.
The marathon lasts longer.
This means there is an energy gap you must bridge while moving. If you don’t, your brain will “pull the plug” on your muscles to preserve vital sugars for your nervous system.
The catch is that eating while running—when your blood is diverted to your muscles and away from your digestive system—is tricky. Your stomach can “shut down” or rebel. That’s why fueling must be planned, not improvised.
The Numbers Game: How Many Carbs Per Hour? (30g, 60g, or 90g?)
Forget the brand for a second and look at the nutrition label. How many grams of carbohydrates are in one gel? A standard gel usually contains about 20–25g.
Sports nutrition science provides clear guidelines:
- Beginner/Intermediate Level: Aim for 30g to 60g of carbohydrates per hour. This translates to roughly one gel every 45 minutes, or two per hour if they are small.
- Advanced Level: Elite or highly trained amateur athletes aim for 90g per hour. A word of caution: absorbing this much requires specific “Gut Training” and products with a precise 2:1 glucose-to-fructose ratio to saturate different intestinal transporters. If you try this tomorrow without practice, stomach issues are guaranteed—and the results won’t be pretty.
My advice? Start by aiming for 40–50g per hour. It’s a safe and effective sweet spot for most runners.
Perfect Timing: Why Waiting for Hunger is a Mistake
The number one rookie mistake is thinking, “I’ll take a gel when I feel tired.”
Too late.
By the time you feel a “bonk” or real hunger, you are already in the red, and it will take significant time for that gel to be digested and hit your bloodstream. You’ve created an energy hole that’s nearly impossible to climb out of.
Fueling must be proactive. You need to eat while you still feel great.
The goal is to maintain steady blood glucose levels, not try to recover them once they’ve crashed.
A Practical Action Plan: Gels at Mile 6, 12, 18…
To keep it simple, create a protocol and follow it like a robot.
Here is a classic strategy example for a marathon (assuming gels with ~25g of carbs):
- Mile 6 (or 40-45 min): First gel. You feel fresh, and it feels unnecessary. Take it anyway.
- Mile 12 (or 1h30): Second gel.
- Mile 18 (or 2h15): Third gel. This is crucial for fending off the Wall.
- Mile 22: Fourth gel (optional, or perhaps one with caffeine for that final mental kick).
If your race time is longer (over 4.5 hours), you’ll need to shorten the intervals and take one every 35–40 minutes.
Water or Sports Drink? How to Wash Down Your Gel
This is where the battle against GI distress is won or lost.
Gels are highly concentrated (hypertonic). To be digested quickly, they must be diluted in the stomach.
If you take a gel with a cup of sports drink (the colorful stuff at aid stations), you create a mixture that is way too sugary. The result? Your stomach pulls water from your body to dilute it, leading to dehydration and nausea.
The Golden Rule: Always take your gel only with plain water.
Rip your gel open 200 yards before the aid station, keep it in your mouth, and wash it down with the water you grab at the table.
Save the electrolytes for the aid stations where you *aren’t* taking a gel. Alternate them.
“Gut Training”: Train Your Intestines Like Your Muscles
Never try anything new on race day. Ever.
The gut is highly adaptable. During your training block, especially on those Sunday long runs, you must perform “Gut Training.”
Use the exact same gels you plan to use on race day. Take them at the same intervals you’ve planned for the marathon.
This accomplishes two things:
- You find out if a specific flavor makes you nauseous after 15 miles.
- You teach your stomach to digest while your body is working, increasing your carb-absorption efficiency.
Stepping up to the start line knowing your nutrition strategy works provides an incredible mental edge. It ensures you won’t run out of gas just when the race really begins.