Ultra Running Fuelling — What to Eat, When and How Much
Most people who blow up in an ultra do not run out of fitness. They run out of calories, or their stomach stops accepting them.
Fuelling is the most trainable and most neglected part of long-distance running. The good news is that the gut adapts the same way legs do — if you practise.
The numbers below are the widely used starting ranges. Individual tolerance varies a lot, which is exactly why you test everything in training rather than on race day.
How much, and how often
| Duration | Carbohydrate per hour | Notes |
|---|---|---|
| Under 90 minutes | Usually none needed | Stored glycogen covers it |
| 90 min – 3 hours | 30–60 g | Start early, don't wait until you feel empty |
| 3+ hours | 60–90 g | Needs mixed carb sources and gut training to tolerate |
Eat little and often — every 20–30 minutes — rather than large amounts occasionally. Set a watch alarm; hunger is an unreliable signal once you're tired.
Hydration and salt
Drink to thirst as the default. Overdrinking is a genuine danger in long events and causes more problems than mild dehydration. In heat, or if you're a heavy or salty sweater, add electrolytes — roughly 300–800 mg of sodium per hour is the usual range, and you'll know you're at the low end if you cramp or feel washed out despite drinking plenty.
Real food versus gels
- Gels and drink mix — fast, precise, easy to carry. Get boring and hard on the stomach after several hours.
- Real food — rice cakes, sandwiches, boiled potatoes with salt, bananas, flapjack. Slower but far more tolerable late on.
- Savoury — after four or five hours most people cannot face anything sweet. Carry something salty; it is often what restarts an appetite.
- Liquid calories — useful when chewing feels like work, which it will.
Train your gut
The gut adapts to carbohydrate load with repeated exposure. Use your long runs to practise: eat the exact products you'll use, at the exact rate, at the effort you'll race at. A stomach that comfortably takes 90 g an hour is built over months, not discovered on the day.
When it goes wrong
- Nausea — slow down. Blood flow to the gut drops as effort rises; easing off is usually what fixes it.
- Can't face sweet — switch to savoury and to liquid calories.
- Bloated and sloshing — stop drinking for twenty minutes and walk. You're absorbing slower than you're consuming.
- Empty and shaky — small amounts frequently, not one big fix. A large intake on an unhappy stomach comes straight back.
Frequently asked questions
How many calories should I eat per hour in an ultra?
Aim for 60–90 g of carbohydrate an hour on runs over three hours, which is roughly 240–360 calories. Build up to the top of that range gradually in training rather than attempting it first on race day.
Should I use gels or real food?
Both. Gels are efficient early on, but most runners cannot stomach them after several hours, so carry real and savoury food for the later stages.
Why do I feel sick when running long?
Most often because effort is too high for the gut to keep absorbing, or because you took in too much at once. Slow down, take smaller amounts more frequently, and keep drinking in sips.
How much should I drink?
Drink to thirst as a baseline and add electrolytes in heat or if you sweat heavily. Forcing large volumes on a fixed schedule causes more problems than it solves.
Where to go next
Want to run this with a guide?
We guide runners of every level on trails across the UK and Europe — routes planned, navigation handled, pace matched to you.