Marathon Fueling: Everything You Need to Know

From carb loading to race-day nutrition, here is how to fuel properly. I learned this the hard way, with 10 gels and 2 heavy bottles in my first race.

By Alex · 10 min read

For my first half marathon at BMO Vancouver, I carried 10 gels and 2 heavy 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 had built, and it told me I needed 3 gels. I did not quite trust it, so I took 5. It turned out that 3 would have been enough. Even I did not believe my own math at first.

That is why I am writing this — so you do not make the same mistakes.

Why Fueling Matters

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

If you take in no fuel during the race, you will run out of glycogen. When that happens you "bonk" or "hit the wall" — a sudden, sharp loss of energy that turns a good race into a long walk to the finish.

Pre-Race Nutrition

Carb Loading (2-3 Days Before)

Carb loading is not about eating pasta until you feel ill. It means:

• Raising your carbohydrate intake to 8-10 g per kg of body weight
• Eating less fiber, so your stomach stays calm
• Drinking enough water

Good carb loading foods:

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

Race Morning (2-4 Hours Before)

Eat a breakfast you know well, with 100-150 g of carbohydrate:

• Oatmeal with a banana
• A bagel with peanut butter
• Toast with jam

Avoid foods high in fiber or fat, which can upset your stomach.

During the Race

The Golden Rules

1. Start early - begin fueling at mile 4-5, not when you already feel 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 30-60 g of carbohydrate per hour. Most gels contain 20-25 g, so that means:

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

Gel vs. Chews vs. Drink

Creating Your Fueling Plan

I built the Fuel Planner because there were no fueling calculators when I was training. How many gels do I really need? I had to work it out myself.

Now you can build your own race-day nutrition plan based on:

• Your target pace
• The race distance
• Where the aid stations are
• The fuel you like

Common Mistakes

1. Carrying too much - like me, with 10 gels. Work out what you need.
2. Skipping breakfast - you need those carbohydrates before the start
3. Starting to fuel too late - once you feel hungry, it is already too late
4. Trying new products - test everything in training first
5. Forgetting electrolytes - losing sodium hurts your 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. Carried out.

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

The Bottom Line

Good fueling will not make you faster than your fitness allows, but bad fueling will definitely make you slower. Plan ahead, practice in training, and follow the plan on race day.

Ready to make your plan? Try our Fuel Planner to get your nutrition right. Do not be the person with 10 gels and 2 bottles, wondering what went wrong.

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