How many carbs per hour in an ultra? Ranges, limits and a worked example

Carbs per hour is the first number in any ultra fuel plan, and the one runners most often guess. Most sports nutrition guidance for long events lands between 60 and 90 grams of carbohydrate an hour, but where you sit in that range depends on how hard you run, how big you are and how much your stomach has learned to take. This guide explains the range, the limits and how to turn it into food.

How many carbs per hour do ultra runners need?#

For events that last more than about two and a half hours, sports nutrition guidance describes up to 90 grams an hour for runners who can absorb it, and 30 to 60 grams for shorter or easier efforts. The position statement from the Academy of Nutrition and Dietetics, Dietitians of Canada and the American College of Sports Medicine is a good place to read the reasoning in full.

Ultra running adds a twist. You are out for many hours, you run slower than in a marathon, and your gut gets tired. A plan that looks fine on paper at hour two can fall apart at hour nine.

What does your body weight and effort change?#

UltraCalcPal starts from body weight and effort, not from a flat number. It uses grams of carbohydrate per kilogram per hour:

• Easy effort: 0.5 g per kg an hour.
• Moderate effort: 0.8 g per kg an hour.
• Hard effort: 1.0 g per kg an hour.
• Very hard effort: 1.2 g per kg an hour.

The idea is simple: a bigger runner who pushes harder burns more fuel and can usually take more of it. A smaller runner on a long, easy day needs less.

What are the limits on carbs per hour?#

Your gut can only absorb so much. A single carbohydrate source, such as glucose or maltodextrin, is absorbed at up to about 60 grams an hour. Adding fructose uses a second pathway, which is why many drink mixes and gels pair the two, usually in a ratio near 60 to 40 glucose to fructose. With both, up to about 90 grams an hour is possible for people who have trained for it.

That is why the app caps a single-source plan at 60 g/h and a glucose plus fructose plan at 90 g/h, and why a sensitive stomach is capped lower still. If you have never taken 90 grams an hour in training, do not start on race day. Build up slowly over several weeks of long runs.

A worked example#

Take a 70 kg runner, moderate effort, out for 12 hours.

• 70 kg x 0.8 g per kg is 56 g of carbs an hour.
• Over 12 hours that is 672 g.
• In food, 56 g an hour is a little over two 25 g gels, which the app rounds up to 3 gels an hour. It is also about two scoops of drink mix, or two gels and half a banana.

Now make it a hard effort: 70 kg x 1.0 is 70 g an hour. That is above the 60 g ceiling for one carbohydrate source, so the plan needs glucose plus fructose, or it needs to settle at 60.

You can try your own numbers in the UltraCalcPal calculator, which shows the hourly amount, the total and what that looks like as real food.

How do you actually eat that much?#

Numbers on a screen do not feed anyone. A few habits help:

1. Eat on a clock. Set a watch for every 20 or 30 minutes and take a small amount each time.
2. Mix sources. Gels, chews, drink mix and solid food together are easier on the gut and on your taste buds than one product for 12 hours.
3. Carry more than you need. Aid-station food is a back-up, not the plan.
4. Expect your appetite to drop. Late in a long race, sweet things can turn your stomach. Salty food and plain carbs can come back into the plan.

The dreaded wall is mostly about running low on stored glycogen, which eating on time helps you avoid.

The figures here are a starting point, not medical advice. Test them in training, and talk to a doctor or dietitian if you have a health condition.

Frequently asked questions#

How many grams of carbs per hour is too many?#

More than your gut can absorb. For one carbohydrate source that is about 60 g an hour, and for glucose plus fructose about 90 g an hour. Going over often shows up as bloating, cramps or nausea.

Is 90 g of carbs an hour realistic for an ultra?#

It can be, for runners who have practised it for weeks and use a glucose plus fructose mix. Many people do better at 60 to 75 g an hour, and that is fine.

Do I need fewer carbs when I run slowly?#

Usually yes. An easy, slow effort burns less, so the per kilogram figure drops. Walking sections and long stops matter too.

Should I count carbs from real food?#

Yes. A banana is about 27 g, a date about 18 g and a small bar about 40 g in the app. Add them to the same hourly total rather than on top of it.

What happens if I fall behind on carbs?#

You can catch up a little, but not all at once. Take a bit more over the next hour rather than a large dose, because a full stomach is the usual cause of a bad patch.