How many carbs per hour in an ultra? Train your gut like you train your legs

A lot of ultra fades blamed on fitness have a fuelling component. The maths is unforgiving: you store roughly 2,000 kcal of usable carbohydrate and you burn multiples of that in a long race. What you absorb per hour, not what you carry, sets your ceiling.

The target range

For races over about three hours, the evidence supports 60 to 90 grams of carbohydrate per hour. Above 90 is an advanced experiment with incomplete evidence, not a requirement. And for most athletes trying to perform over a long day, sitting below 40 g/h is leaving a lot on the table.

The gut is trainable

Absorption improves with practice, the same way legs do. Every long run is a fuelling rehearsal: fixed grams per hour, starting in the first 30 to 45 minutes, not when you feel empty. By then you are already behind.

• Start where your gut is, not where the elites are. 40 to 60 g/h if you're new to it.
• At higher intakes, use more than one carbohydrate source: glucose or maltodextrin plus fructose, because they use different doors out of the gut. 2:1 works, but it isn't a law. Different ratios can work well, and your gut tolerance matters more than defending one formula.
• Practise the exact products, flavours and textures you'll race with. Flavour fatigue at hour seven is real.
• Log it. Grams per hour and a gut score out of ten, every long run.

Before and after matter too

Long runs start fuelled: carbohydrate the night before, then 30 to 60 grams in the hour before an early start. A fasted 24-miler teaches you nothing except what running on empty feels like, and it costs you days of recovery. Afterwards, a carbohydrate-rich meal with 25 to 35 grams of protein starts the repair.

The rule that overrides everything

If a fuelling test says you tolerate 90 g/h for two hours, but three four-hour long runs at 90 have wrecked your stomach, the long runs win. The best plan is the highest intake you can absorb reliably while moving at race effort. Find that number in training, then defend it on race day.

What I watch

• Grams of carbohydrate per hour, actually logged, not intended.
• Gut tolerance: the score out of ten, and what broke it.
• When in the run energy or pace begins to fade.
• Whether the race-day strategy has been rehearsed enough times to trust.

That's the information. The decision, what to change and when, comes from putting it next to the rest of your training.

Evidence level: the 60 to 90 g/h range and gut trainability are well supported; intakes above 90 are increasingly used by elites but the performance evidence remains limited. One warning: drink to thirst, and never treat sodium as permission to overdrink. Overdrinking is the dangerous hydration error in ultras.