Quick summary
- Carbohydrate: aim for 60 g per hour; well-practised runners can take up to 90 g per hour using gels that mix glucose and fructose.
- Timing: start 25–40 minutes in, then little and often: about every 20–30 minutes.
- Sub-4 example: about 215 g of carbohydrate, or roughly 6 gels if you also drink sports drink at aid stations (about 9 if gels only).
- Fluid: drink to thirst, typically 400–800 ml per hour. Don't drink so much that you gain weight.
- Practise: use your exact race-day plan on every long run.
Most runners who "hit the wall" don't lack fitness. They run out of fuel. Your muscles store enough carbohydrate for roughly 90–120 minutes of hard running, and a marathon takes longer than that for almost everyone. The fueling plan is how you cover the gap.
Why you need carbohydrate during a marathon
At marathon effort, your body burns a mix of fat and carbohydrate. Fat stores are huge, but fat can't be burned fast enough to sustain race pace on its own. Carbohydrate is the limiting fuel.
When stored carbohydrate (glycogen) runs low, usually after 30 km, pace drops sharply, legs feel heavy and thinking gets foggy. Taking carbohydrate during the race slows that depletion, so you can hold pace for longer.
How much carbohydrate per hour
Sports-nutrition guidance for events lasting more than about 2.5 hours suggests up to 90 g of carbohydrate per hour. In practice:
- 60 g per hour is a realistic target for most marathoners and what the table below uses.
- 75–90 g per hour is possible with practice, using products that combine glucose and fructose, which the gut absorbs through different routes.
- Below 40 g per hour is usually not enough for a full marathon.
Your gut adapts to carbohydrate the way your muscles adapt to training. If you take nothing on long runs, 60 g an hour on race day will feel hard on your stomach.
Fueling by finish time
This table assumes 60 g of carbohydrate per hour, starting about 25 minutes in and finishing about 15 minutes before the end, with 25 g gels. Sports drink at aid stations typically adds around 20 g per hour, which is why the "with sports drink" column needs fewer gels.
| Finish time | Total carbohydrate | Gels if gels only | Gels with sports drink at aid stations | One gel about every |
|---|---|---|---|---|
| 3:00 | about 155 g | 6 | 4 | 25 min (gels only) / 35 min (with drink) |
| 3:30 | about 185 g | 7 | 5 | 25 min / 35 min |
| 4:00 | about 215 g | 9 | 6 | 25 min / 35 min |
| 4:30 | about 245 g | 10 | 7 | 25 min / 35 min |
| 5:00 | about 275 g | 11 | 7 | 25 min / 35 min |
| 5:30 | about 305 g | 12 | 8 | 25 min / 35 min |
Check the label on your gels: carbohydrate content ranges from about 20 g to 45 g per gel, so adjust the count to match. If you're aiming for your finish time, take your pace from our marathon pace chart.
A sample sub-4 fueling timeline
For a 3:58 finish with 25 g gels and sports drink at aid stations:
| Race time | Approx. distance | Take |
|---|---|---|
| 0:30 | 5 km | Gel 1 with water |
| 1:05 | 11 km | Gel 2 |
| 1:40 | 18 km | Gel 3 |
| 2:15 | 24 km | Gel 4 |
| 2:50 | 30 km | Gel 5 |
| 3:20 | 35 km | Gel 6 |
| Every aid station | A few mouthfuls of sports drink or water, to thirst |
Take gels just before an aid station so you can wash them down with water. The full 16-week sub-4 training plan builds this practice into the long runs.
Fluid and sodium
Fluid: most runners do well drinking to thirst, which typically works out at 400–800 ml per hour depending on temperature, body size and sweat rate. To estimate your own needs, weigh yourself before and after a 60-minute run without drinking: each kilogram lost is about one litre of sweat.
Don't overdrink. Drinking far more than you sweat can dilute blood sodium (hyponatremia), which can be dangerous. If you weigh more after a long run than before it, you drank too much.
Sodium: in warm conditions or if you're a salty sweater (white marks on your kit), aim for roughly 300–600 mg of sodium per hour from electrolyte drinks, salty gels or capsules. See our guide to marathon training in hot weather.
Race morning
- 2–4 hours before the start: a familiar, carbohydrate-rich breakfast, about 1–2 g of carbohydrate per kg of body weight (70–140 g for a 70 kg runner). Porridge, bagels with jam, rice or bananas work well.
- Avoid: high-fibre, high-fat and very spicy foods.
- 15 minutes before the start: an optional gel with a few sips of water.
Training your gut
- From about 12 weeks out, take carbohydrate on every run longer than 90 minutes.
- Start at 30–40 g per hour and build by about 10 g per hour every couple of weeks.
- Use the exact gels and drinks you'll use on race day, ideally the brand served on the course.
- Practise at marathon pace, not just easy pace. Digestion is harder at higher effort.
FAQ
How many gels should I take in a marathon?
Most runners need 6–12 gels depending on finish time and whether they also drink sports drink. A sub-4 runner typically needs about 6 gels with sports drink at aid stations, or about 9 gels if relying on gels alone.
When should I take my first gel in a marathon?
Take the first gel about 25–40 minutes into the race, then one roughly every 20–35 minutes. Don't wait until you feel tired; by then you're already running low.
Can I fuel a marathon with real food instead of gels?
Yes, if you've practised it. Bananas, dates, chews and sweets can all work. Gels are popular because they're compact and fast to digest, not because they're required.
What causes stomach problems during a marathon?
Common causes are taking more carbohydrate than your gut is trained for, very concentrated gels without water, high-fibre or fatty food beforehand, dehydration and heat. Practising your fueling on long runs reduces the risk.
Do I need electrolytes during a marathon?
Many runners benefit from extra sodium in hot conditions or if they sweat heavily. In cool weather, sports drink at aid stations is often enough.
This article is general information, not medical or nutrition advice. If you have diabetes, a digestive condition or other health concerns, check with a doctor or registered dietitian before changing how you fuel.