Carbs per hour ultra trail: what the UTMB 2025 guideline tells you

The UTMB 2025 organization uses 40-80g carbs per hour as the official fueling guideline for ultra trail runners. Two Eagle fruit performance bars provide exactly 40g of carbohydrates — the lower limit of that target zone — in a format that digests during movement.

What does the UTMB 2025 guideline mean for your fueling?

The Mont-Blanc circuit spans up to 171 kilometers and 10,000 meters of elevation gain. The fastest finishers take 20 hours. Most participants run for 30 to 46 hours. This makes UTMB not a race where you fuel once — it's a long-term logistical challenge concerning fuel, digestion, and pace.

The official UTMB 2025 guideline explicitly states: 40 to 80g of carbohydrates per hour depending on intensity, running time, and individual tolerance. Those who stay below 40g risk glycogen depletion after 60 to 90 minutes of effort. Those who exceed 80g without a trained gut risk gastrointestinal problems — the most common cause of DNF among ultrarunners.

Carbs per hour in ultra trail is therefore not a preference. It's an operational decision with a direct impact on your finish.

Why digestibility in ultra trail weighs heavier than in cycling

Cyclists and ultrarunners both burn carbohydrates. But the physiological context differs fundamentally. In cycling, the torso remains relatively stable. Blood flows relatively efficiently to the digestive system, even during high intensity.

Running is different. Every step generates vertical impact. The intestines move along. At intensities above 70% of maximum heart rate, blood flow to the gastrointestinal tract significantly decreases. Undigested food remains. And during a 40-hour effort, this problem accumulates.

Three factors make digestibility the critical variable in ultra trail:

• Impact per step compresses the stomach and increases the risk of nausea
• Longer duration means more cumulative stress on the digestive system
• Varying intensity — climbing, descending, flat — makes a consistent absorption rate harder to plan

That's why portion size is not a detail. It's strategy.

How does the 2:1 glucose/fructose ratio work during an ultra?

The human body has two primary transporters for carbohydrates from the intestine to the blood: SGLT1 for glucose and GLUT5 for fructose. Both transporters have a maximum capacity. Glucose alone maximizes at approximately 60g per hour. Fructose alone is even lower.

If you combine both in a 2:1 ratio, you use both transporters simultaneously. The result: a theoretical maximum absorption of 90g of carbohydrates per hour without increasing gastrointestinal discomfort — provided the gut is trained.

Eagle Nutrition formulates each fruit performance bar with a 2:1 glucose/fructose ratio. No artificials. No synthetic sugars. The ratio is derived from fruit — the most direct source of mixed carbohydrates in nature.

For ultra trail runners operating in the 60-80g zone, this ratio is functional: you maximize absorption without overloading your gut with simple sugars.

How many carbs do you need per hour at UTMB intensity?

The target zone of 40-80g per hour is not a fixed value — it is a range. Where you fall within that range is determined by three variables:

• Running intensity: At higher intensity (technical climb, steep descent), carbohydrate consumption increases. At walking pace, it decreases.
• Running time so far: After 10 hours of effort, glycogen status is reduced. The pressure on external carbohydrate intake increases.
• Gut training: An untrained gut tolerates a maximum of 60g per hour. A trained gut can handle 80-90g.

Practically translated: someone aiming for 60g per hour without gastro-risk uses two to three Eagle fruit performance bars — each 25g, each with 20g of carbohydrates — distributed over the hour. That's an intake every 20 to 30 minutes.

Why Eagle's 25g format is functional during ultra trail

Larger portions — a 60g gel, a 90g bar, a full bag of dried fruit — require more digestion per intake moment. The stomach has to process more, slower gastric emptying, higher concentration of sugars in the small intestine. At low intensity, this is manageable. At hour 20 of a UTMB run, with 8,000 meters of elevation gain in the legs, this is risky.

A 25g fruit performance bar delivers 20g of carbohydrates in a solid, chewable form. Chewability is functional: it activates saliva production and the initial phase of digestion even before the food reaches the stomach. Gels do not do this. A 25g format is also practical in cold, rain, or fatigue — no sticky hands, no empty wrapper flapping.

Nutrition during ultra trail UTMB must work in all conditions. Format is therefore not an aesthetic choice. It is a fueling decision.

How do you plan your carb intake over 20-46 hours of UTMB?

A fueling plan for UTMB starts from three fixed parameters: hourly target zone, available replenishment points, and gut tolerance. The official UTMB courses have aid stations at fixed distances — on average every 15 to 25 kilometers depending on the race.

Between posts, you are self-sufficient. This means that the intake you carry with you is the only one that counts. A practical framework:

• Hours 1-6: 40-60g per hour. Glycogen is still available. Priority: build rhythm and activate the gut.
• Hours 6-20: 60-80g per hour. Glycogen reserves decrease. External intake becomes the primary fuel source.
• Hours 20+: 40-60g per hour. Fatigue reduces intensity. Digestive tolerance decreases. Smaller, more frequent portions work better than large ones.

Two Eagle fruit performance bars per hour deliver 40g of carbs and 50g total weight. For a 10-hour block between aid stations, that's 20 bars — 500g of weight. Compact for the fuel it delivers.

Eagle fruit performance bar versus gel: what do you choose during ultra trail?

Gels have dominated ultra trail fueling for years. The reason is understandable: quick to consume, quickly absorbed, light. But the downside is equally real.

Criterion	Gel (standard)	Eagle fruit performance bar
Portion size	30-40g per sachet	25g per bar
Carbohydrates per portion	20-25g	20g
2:1 ratio	Depends on brand	Standard in every format
Chewability	None	Full
Artificials	Often present	None
Format in cold/fatigue	Sticky, hard to open	Dry, directly edible
Taste sensation after 20 hours	Nauseating for many	Fruity, less flavor fatigue

No single format is universally superior. But for ultrarunners who run 30+ hours and are looking for clean fuel without artificials, the Eagle fruit performance bar offers a functional addition or complete alternative to gels.

What is flavor fatigue and why does it matter at UTMB?

After 15 to 20 hours of exertion, taste perception changes. What tastes neutral or sweet in hour one becomes intense and sometimes nauseating in hour twelve. This phenomenon — flavor fatigue — is documented in ultrarunners and is a primary reason why athletes stop eating during nighttime hours.

A non-eating athlete does not refuel. A non-refueling athlete does not achieve 80g of carbs per hour. The result is an energy peak followed by a progressive decline in performance — not dramatic, but consistent.

Fruit-based fuel offers a flavor profile that is more sustainable for most athletes than synthetic sweeteners or highly concentrated gel flavors. Eagle fruit performance bars contain no artificials — flavor comes exclusively from fruit and functional ingredients. This positions them factually differently from most gels on the market.

How to train your gut for 80g carbs per hour?

Gut training — also known as intestinal training — is a proven approach to increase the absorption capacity of carbohydrates. The principle: by repeatedly taking higher amounts of carbs during training, the gut adapts its transport capacity.

Practical approach for UTMB preparation:

• Start 8-12 weeks before race day with conscious carb intake during long training sessions
• Begin at 40g per hour and increase weekly by 10g until your target zone is reached
• Train with the exact format you will use during the race — no surprises on race day
• Combine solid food and liquid in training sessions of 3+ hours to simulate real race conditions

Those who try 80g per hour for the first time on race day risk gastrointestinal problems. More about gut training for ultrarunners can be found in the Eagle knowledge base.