Fueling for Your Marathon
March 4, 2026 — 15 min read
Fueling may be intimidating if you're just starting out. Or maybe you haven't thought much about it at all — that was me before my first marathon. Here's everything I wish I knew.
Why fueling matters (the math)
Your body has a fuel tank. It's called glycogen — stored carbohydrates in your muscles and liver.
Most people can hold around 400–500 grams worth. That sounds like plenty for a marathon. It's not.
At marathon effort, performance starts falling apart long before the tank is truly empty (research suggests the average runner will hit "the wall" around 75–90 minutes without external fuel).
Your body does burn fat alongside carbs, but fat can't keep up with the demand at marathon pace.
As your stored carbs drop, your brain starts pulling the emergency brake — "the bonk."
This is where the importance of external carbs comes into play.
Eating during the race
Eating during the race does three things:
- It slows down how fast you burn through your glycogen stores
- It keeps your blood sugar stable so your brain stays in the game
- It extends the window before everything falls apart
Through both your stored carbs and fueling throughout the marathon, you're giving your body the best chance to make it to the finish line.
The protocol that actually works
When to start
First fuel should be consumed at minute 15. Not mile 5. Not when you "settle in."
This feels absurd when your legs feel great. Do it anyway. You're eating for mile 20.
How often
Every 20 minutes after the first consumed fuel. Small, frequent doses keep your gut comfortable.
How much per dose
Take your hourly target and divide by 3.
How many carbs per hour?
This depends on your experience with fueling, not your fitness level.
Carbs Per Hour by Experience
< 6 months
30–45 g/h
Your safe baseline. Focus on nailing the timing before worrying about the amount.
6–18 months
45–60 g/h
Where most first-time marathoners should race.
18+ months
75–90 g/h
The performance range. You need to have built up to this over months.
For most people running their first marathon at moderate effort, 45–60 g/h is the target.
Sodium — the piece most people skip
Sodium isn't just about cramps. Your gut literally uses sodium to absorb the carbs you're taking in.
A rough guide based on how much you sweat:
Low sweater
~400 mg/h
You rarely see salt on your gear.
Moderate sweater
~700 mg/h
Some salt marks on your hat or shirt.
Heavy sweater
~1,000 mg/h
White crust on gear, eyes sting.
If it's a hot day (above 77°F / 25°C), multiply your target by about 1.25×.
For a first marathon, ~700 mg/h is a solid default.
For a deeper dive: Sodium Isn't Just for Cramps.
Race week (the part nobody talks about)
Fueling doesn't start at the gun. Here's what the week before looks like:
7 days out
Start marginally increasing carbs at meals.
3 days out
Peak carb loading. Target 8–10g of carbs per kg of body weight.
2–1 days out
Pre-load sodium. Add 800–1,000mg extra sodium across the day.
Night before
Familiar, high-carb, low-fiber meal. Zero experimentation.
Race morning (2–3h before)
Target 75–100g of simple carbs.
2 hours before
Sip water with electrolytes. Small sips, ~500ml total.
15 minutes before
Stop drinking. Empty your bladder. Start the fueling protocol at minute 15 of the race.
Train your gut (this is non-negotiable)
Most first-timers skip fueling on training runs, then try to eat on race day and their stomach falls apart.
When you're running, blood flow shifts away from your digestive system. That takes practice.
The good news: your gut adapts faster than you'd think.
Practice once per week on your long run. Here's a rough progression:
Liquid only — sports drink or diluted carb mix.
Introduce gels or chews.
Building toward your race target.
Practice at race intensity.
You've hit your target comfortably in training.
Zero GI distress on a long run = you're cleared to bump up next week.
Any symptoms = stay at the current level.
For the full protocol, see The Gut Training Protocol.
GI distress troubleshooting
If stuff goes sideways during a training run, here's what it usually means:
Bloating / fullness
Cause: Taking too much at once.
Fix: Go smaller doses at the same frequency.
Sloshing stomach
Cause: Not enough sodium, too much liquid.
Fix: Try switching from drink-based carbs to gels.
Nausea
Cause: Started fueling too late or dose is too high.
Fix: Dial back amount, tighten timing.
Lower GI urgency
Cause: Gut isn't tolerating something.
Fix: Drop back a level and try a different product.
None of this means you're broken. It means you're learning what your gut can handle.
You don't need expensive products
One energy gel is ~20–30g of carbs. But so is 1 tbsp of honey with a pinch of sea salt (~20g). Cost per "gel" drops from $2–4 to maybe 30 cents.
There are other simple ways to bring fueling costs down such as buying ingredients in bulk.
Bring it home
The runners who look strong at mile 24 aren't more talented. They just figured this stuff out before the race started.
Everything above gets you 90% of the way there. Nail the basics — fuel early, stay consistent, include sodium, train your gut.
Or let PODIUM do the thinking for you
Everything above is doable on your own. But it's a lot to keep track of when you're mid-race.
That's why I built PODIUM. You tell it your workout — duration, intensity, sport — and it calculates your carb and sodium needs, then tells you when to fuel with audio cues.
Want the cheat sheet?
I put together a one-page PDF with the fueling protocol, gut training progression, and race week timeline.
GET THE PLAYBOOK