Carb Loading for a Marathon: What Actually Works (From Someone Who’s Messed It Up + Nailed It)

If you’re running a marathon this year, especially something like London, here’s a high chance you’re overthinking carb loading.

And I get it.

Because carb loading sits in that weird space where:

• The science is clear

• But the execution feels confusing

• And the fear around carbs is still very real

So in this blog, I’m going to break it down properly.

Not just the what, but the how, based on:

• Coaching hundreds of women

• My MSc in Sports Nutrition

• And honestly… my own trial and error across 2 marathons and 1 ultra

Because the truth is: It’s not carbs that ruin your race, it’s how you use them.

First: Why Carb Loading Actually Matters

Carbohydrates get broken down into glucose and stored as glycogen in your muscles and liver.

That glycogen is your main fuel source for:

• Running at pace

• Sustaining effort

• Avoiding that dreaded “wall”

The issue?

You can only store roughly 90–120 minutes worth of glycogen.

And a marathon is… longer than that.

So what happens when you run out?

• Energy drops

• Pace drops

• Everything feels harder

• Your body switches to fat (which is slower and less efficient)

That’s the wall.

And here’s the part most people miss:

👉 Women are more likely to:

• Start under-fuelled

• Deplete glycogen faster

• Fear carbs more

Which is why so many women don’t just hit the wall…They hit it earlier than they need to.

What Carb Loading Is (And What It’s Not)

Let’s clear this up first.

Carb loading is NOT:

• A massive pasta dinner the night before

• Eating everything in sight

• “Earning” your carbs

• Cramming 200g carbs into one meal

Carb loading IS:

• Increasing carbohydrate intake over a few days

• While training volume drops

• To fully top up glycogen stores before race day

That’s it.

The Scale Will Go Up (And That’s a Good Thing)

This is where most women panic.

When you carb load:

• 1g carbohydrate stores with ~3–4g water

So yes 👉 You might gain 1–3kg

But this is:

• Stored fuel

• Hydration

• Performance support

Not fat.

If the scale goes up? 👉 You’ve probably done it right.

The Biggest Mistake I Made (And See All The Time)

My first marathon?

I did everything “right” on paper:

• High carbs

• Followed guidelines

• Fully committed

But I:

• Overtrained

• Overfuelled

• Didn’t personalise anything

Result?

👉 3 toilet stops during the race

And it wasn’t because I under-fuelled.

It was because: My timing was completely off.

The Real Game Changer: Timing

During my ultra training block, I realised something:

👉 I wasn’t bad at fuelling

👉 I was bad at timing my fuelling

Example:

I was smashing:

• 100g carbs (scotch pancakes + syrup)

• 30 minutes before a run

And wondering why my stomach was in bits.

It wasn’t a carb issue.

👉 It was a timing issue

What You Need to Know About Timing

1. Pre-Run Fueling

If you’re running early:

• Go lighter before

• Don’t force a huge meal

Think:

• Banana

• Toast

• Small carb snack

Then 👉 Fuel earlier INTO the run

2. Delaying Carbs = More Gut Issues

This is a big one.

A lot of women:

• Delay gels

• Avoid carbs early

• Try to “hold out”

But what actually happens?

👉 Your body is:

• Stressed

• Under-fuelled

• Under-hydrated

So when you finally eat?

👉 Your stomach panics

👉 You get cramps, urgency, or “dodgy stomach”

It’s not the gel. It’s the timing.

3. Hydration Matters More Than You Think

Gels without water?

👉 Recipe for gut issues.

You need:

• Regular sips

• Consistent hydration

• Not just “when you feel thirsty”

Carb Loading Strategy (Simple Version)

If your race is Sunday:

Early Week:

• ~3–5g carbs per kg bodyweight

• Build gradually

Friday:

• Higher carb day (~5–7g/kg or more if experienced)

Saturday:

• Slightly reduce (but still higher than normal)

• Focus on digestion + feeling good

Important:

If you usually eat 150–200g carbs…

👉 Do NOT jump straight to 600g

Instead:

• Increase gradually

• Choose easy-to-digest carbs

• Work within what your body can handle

The Protein & Fat Mistake

If you’re a “high protein girly”…

This is where you need to shift.

Carb loading ≠ calorie loading.

If protein + fats stay too high:

• You’ll feel full

• You won’t hit carb targets

• You’ll feel heavy + sluggish

Instead:

• Prioritise carbs

• Reduce fats slightly

• Let protein sit at a moderate level

What Happens When You Get It Right

For me?

• 35 minute marathon PB

• No toilet stops

• Completed my first ultra

• 8th female, 52nd overall

And the biggest shift wasn’t 👉 Doing more

It was 👉 Understanding my body

Race Day: Keep It Simple

Before:

• Easy carbs

• Familiar foods

• Nothing new

Example:

• Bagel + syrup

• Juice or sports drink

If nervous 👉 Go smaller, more frequent

During:

• Aim: ~60g carbs per hour (more if trained)

• Start early (don’t wait)

• Take gels with water

Final Message

The runners who improve the most aren’t chasing perfect races.

They:

• Learn

• Reflect

• Adjust

• Go again

It’s okay if things don’t go to plan.

But ask yourself 👉 Did I follow guidelines… but ignore what works for ME?

If You’re Racing Soon…

You’ve done the hard work.

Now:

• Fuel properly

• Trust your body

• Be present

• Enjoy it

Because this race?

👉 It’s not just a finish line

👉 It’s the result of everything you’ve built

Want help with your fueling?

DM me “FUEL” on Instagram and I’ll send you my full race fueling guide.

Or reach out if you want 1:1 support, this is exactly what I help women master.

You deserve to feel strong, fuelled, and confident on race day 🤍