Marathon Fueling: Everything You Need to Know

From carb loading to race-day nutrition, here's how to fuel properly. I learned this the hard way—10 gels and 2 clunky bottles my first race.

By Alex · 10 min read

My first half marathon at BMO Vancouver, I brought 10 gels and 2 clunky water bottles. I had no idea what I actually needed. I just wanted to prove I could do something hard.

I finished in 3:01:00 and spent the next week barely able to walk down stairs.

A year later, I used the fuel planner I'd built, and it told me I needed 3 gels. I didn't fully trust it, so I brought 5. Turns out, 3 would've been enough. Even I didn't believe my own math at first.

That's why I'm writing this—so you don't make the same mistakes I did.

Why Fueling Matters

Your body stores about 2,000 calories of glycogen (stored carbs) in your muscles and liver. A marathon burns approximately 2,600-3,000 calories. A half marathon burns about 1,300-1,500.

Without taking in fuel during the race, you will run out of glycogen. When that happens, you "bonk" or "hit the wall"—a sudden, dramatic loss of energy that can turn a great race into a survival march.

Pre-Race Nutrition

Carb Loading (2-3 Days Before)

Carb loading isn't about eating pasta until you're sick. It's about:

  • Increasing carb intake to 8-10g per kg of body weight
  • Reducing fiber to avoid GI issues
  • Staying well-hydrated

Good carb loading foods:

  • White rice and pasta
  • Bread, bagels, English muffins
  • Potatoes (without skin)
  • Bananas
  • Sports drinks

Race Morning (2-4 Hours Before)

Eat a familiar breakfast with 100-150g of carbs:

  • Oatmeal with banana
  • Bagel with peanut butter
  • Toast with jam

Avoid high-fiber, high-fat foods that could cause stomach issues.

During the Race

The Golden Rules

  1. Start early - Begin fueling by mile 4-5, not when you're already hungry
  2. Stay consistent - Take fuel every 20-30 minutes
  3. Practice in training - Never try anything new on race day

How Much to Take

Aim for 30-60g of carbs per hour. Most gels contain 20-25g, so that's:

  • 1 gel every 20-30 minutes, OR
  • Equivalent from sports drink, chews, or real food

Gel vs. Chews vs. Drink

Creating Your Fueling Plan

I built the Fuel Planner because fueling calculators didn't exist when I was training. How many gels do I actually need? I had to do the math myself.

Now you can create a personalized race-day nutrition strategy based on:

  • Your target pace
  • Race distance
  • Aid station locations
  • Preferred fuel sources

Common Mistakes

  1. Bringing too much - Like me with 10 gels. Calculate what you need.
  2. Skipping breakfast - You need those pre-race carbs
  3. Starting fuel too late - By the time you're hungry, it's too late
  4. Trying new products - Test everything in training
  5. Ignoring electrolytes - Sodium loss affects performance

What I Do Now

For my 2:06 half marathon, I had a plan:

  • Gel at km 7
  • Gel at km 14
  • Water at every aid station

Simple. Practiced. Executed.

No bonking. No regrets. I crossed the line smiling instead of limping.

The Bottom Line

Proper fueling won't make you faster than your fitness allows, but improper fueling will definitely make you slower. Plan ahead, practice in training, and execute on race day.

Ready to create your plan? Try our Fuel Planner to dial in your nutrition strategy. Don't be the person with 10 gels and 2 bottles wondering what went wrong.