How do I fuel?
Your race-day carbs, fluid and sodium per hour, turned into how many gels (or which bottle) it actually takes, plus carb-loading and an aid-station plan. So race day is rehearsed, not a gamble.
From your coach
“For a 3:14:40 marathon on the standard target, that's about 90 g of carbs an hour, roughly 4.1 gels, or one high-carb bottle topped up with a gel. Start in the first few miles, not when you're already empty, and rehearse it on your long runs so your gut is ready.”
Carbs
90g/hr
Standard
≈ Gels
4.1/hr
at ~22 g each
Total carbs
290g
over ~3.2 hr
Fluid
500ml/hr
to thirst
Sodium
400mg/hr
sweat-dependent
Carb-load
560–840g/day
1–2 days before
Modern guidance is up to ~90 g/hr for a trained gut on a three-hour-plus day (from glucose-and-fructose mixes), and 100–120 g/hr only after weeks of gut training. The guide below breaks down the fuels, carb-loading and aid stations.
Lock this in.
Turn this into a full plan, then have a coach watch every run.
The marathon is a fuel problem.
Most marathons aren't lost on fitness; they're lost on an empty tank. You can only store about 90 minutes of carbohydrate; the rest you have to take in as you run. Here's exactly how much, in what, and when.
What the wall actually is
Your muscles and liver hold roughly 90 minutes to two hoursof hard running as stored carbohydrate (glycogen). Run a marathon and you’ll need far more than that. “The wall”, that mile-20 lurch where the pace falls off a cliff, is simply the moment the tank runs dry and your body is forced onto fat, which can’t release energy fast enough to hold race pace.
The fix isn’t to run slower. It’s to keep topping the tank up from the start, so you never reach empty. Get this right and the last 10K stops being a survival exercise. Get it wrong and no amount of training saves the day.
Then versus now
Fuelling advice has changed more in the last decade than in the thirty years before it. If you learned the old numbers, they’re holding you back.
Traditional
30–60 g/hr
Built on a single sugar (glucose), which the gut can only absorb at about 1 gram a minute before it saturates. For decades, 60 g/hr was the ceiling.
Modern
up to 90–120 g/hr
Combine glucose and fructose(roughly 2:1) and you open a second absorption pathway. A trained gut clears ~90 g/hr; elite runners now fuel at 100–120.
Gut training is the catch
How much, by how long you're out
Carbohydrate need is driven by time on your feet, not your bodyweight, and capped by what your gut can take. Pick the row that matches your finish time, then choose a target you’ve actually trained.
| Time on course | Carbs per hour | Notes |
|---|---|---|
| Under 2 hr | 30–60 g | Single or dual-source both fine. |
| 2–2.5 hr | ~60 g | Dual-source starts to pay off. |
| 2.5 hr+ (most marathons) | 60–90 g | Glucose + fructose. 90 needs a trained gut. |
| Trained / elite | 90–120 g | Only after weeks of gut training. |
What to carry
Gels
20–25 g (40 g for doubles)
The default. Fast to absorb, easy to carry, easy to time. Wash them down with water; most aren't isotonic.
Drink mix
40–80 g per bottle
The quiet workhorse. One high-carb bottle carries most of an hour's carbs plus fluid and sodium together, far gentler on the gut than stacking gels.
Chews & blocks
22–24 g per serving
Slower to absorb and more chewing than you want at pace, but some stomachs prefer them. Useful early, less so late.
Real-food gels
21–45 g
Whole-food blends (fruit, oats, nut butter). Easier on a sensitive gut for some; thicker and slower for others. Test them.
Caffeine
How many gels is that, really?
This is where targets become a race plan. A standard gel is about 22 grams; the “double” gels carry 40. Here’s what common marathon brands actually deliver:
| Gel | Carbs |
|---|---|
| GU Energy Gel | 22 g |
| SiS GO IsotonicNo water needed | 22 g |
| Maurten Gel 100Hydrogel | 25 g |
| Neversecond C30 | 30 g |
| Precision PF 30 Gel | 30 g |
| Maurten Gel 160Double | 40 g |
| SiS Beta Fuel GelDouble | 40 g |
| Precision PF 90 GelA full hour | 90 g |
So to hit your hourly target, you’re choosing between a pocketful of gels or one concentrated bottle plus a top-up:
| Target | In gels | Or by bottle |
|---|---|---|
| 60 g/hr | ~3 standard gels | one 40 g bottle + a gel |
| 90 g/hr | ~4 standard gels | one 80 g bottle + a small top-up |
| 120 g/hr | gut-trained only | one 80 g bottle + two 40 g gels |
For most runners the bottle route is kinder on the stomach: a single high-carb drink mix carries fluid, carbs and sodium together, with fewer concentrated hits to digest. The numbers on the big mixes:
| Drink mix | Carbs | Per |
|---|---|---|
| Maurten Drink Mix 320 | 80 g | 500 ml |
| SiS Beta Fuel 80 | 80 g | 600 ml |
| Maurten Drink Mix 160 | 40 g | 500 ml |
| Tailwind Endurance Fuel · 3 scoops | 75 g | 750 ml |
Carb-loading, the modern way
The old “deplete yourself then load” ritual is gone. The current evidence is simpler and kinder: in the 1–2 days before the race, eat 8–12 grams of carbohydrate per kilogram of bodyweight a day while you taper. That tops up muscle glycogen above its normal level and is worth a couple of percent on race day: a few free minutes.
For a 70 kg runner that’s roughly 560–840 grams a day , more than it sounds. The trick is to do it without feeling stuffed:
- Go white, not wholemeal. White rice, pasta, bread, bagels and potatoes. This is the one week to skip the fibre; it just fills you up and risks race-morning trouble.
- Drink some of it. Fruit juice and sports drinks hit the target with far less bloat than another plate of pasta.
- Five or six small feeds beat two big blowouts. Keep fat and heavy protein down on loading days, they slow you up and crowd out carbs.
- Nothing new.Race week is not the time to try a cuisine your gut hasn’t met. Hydrate well, glycogen is stored with water.
The night before
An aid-station plan
Big-city marathons put water and sports drink roughly every mile or two, twelve to fourteen-plus stations. Some place gels at set points (Boston and New York stock Maurten depots around miles 12–21), but supply runs out and brands vary. The rule: carry 70–80% of your own fuel and use the course for fluid.
- Take a gel just before a water station, not after. Gels are concentrated, the water right behind it helps it empty from your stomach and heads off nausea.
- Pinch the cup and walk a few steps. Fold the rim to a spout, take ten seconds, sip rather than gulp. The time lost is nothing; the fluid you actually keep down is everything.
- Don’t skip sodium. Water alone over four hours invites cramp, and, if you over-drink it, something more dangerous. Make sure your plan includes salt, from the sports drink or your own mix.
- Never try anything new on race day.If a station offers a gel you haven’t trained with, skip it. The only thing that’s always safe is water.
From your coach
“A gut is trained, not born. The runners who fuel beautifully on race day spent twelve weeks rehearsing the exact same gels, the exact same bottle, on their long runs. Build your plan from the number above, then practise it until race day is just another Sunday.”
Methodology & sources
Carbohydrate targets follow current sports-nutrition consensus (multiple-transportable carbohydrate at ~2:1 glucose:fructose; up to ~90 g/hr for >2.5 h, 90–120 g/hr with gut training). Product figures are per single serving as sold and verified against brand pages (2025–26). Personalise fluid and sodium with a sweat test: individual losses vary widely.