70g carbohydrates per hour trail running: how to build your fueling system

 

On the trail, every kilojoule counts. For efforts longer than 90 minutes, you need external carbohydrates. The standard: 70g of carbohydrates per hour of trail running as a starting point for a 50K ultra. This is how you build that system. The complete guide to energy bars for endurance sports provides the broader context. Here, I'll focus on the specific plan for the trail.

Why do you need 70g of carbohydrates per hour during trail running?

Your muscles primarily burn carbohydrates at moderate to high intensity. The glycogen stores in muscles and liver average 400 to 500g, enough for 60 to 90 minutes of intense effort. After that, output declines if you don't refuel. On a 50K ultra, you run for four to seven hours. If you wait to eat, you'll pay for it later.

Sports nutrition science considers 60g of carbohydrates per hour as a lower limit for efforts up to three hours. Above three hours, for trained athletes with a good fueling protocol, the recommendation increases to 70g to 90g per hour. The difference lies in gut capacity and carbohydrate type. This is where the 2:1 glucose/fructose ratio plays a crucial role.

Glucose is absorbed via a primary transport channel in the gut (SGLT1). This channel is saturated around 60g per hour. Fructose uses a separate channel (GLUT5). By combining both sugars in a 2:1 ratio, you use both channels simultaneously. Result: more fuel, fewer stomach problems, better sustained pace. King et al. (2019) showed that 90g/hour glucose-fructose 2:1 led to the best time trial performance after three hours of submaximal effort, with 6.8% more power than 100g/hour and 4% more than 80g/hour.

What is the difference between a fruit performance bar, gel, and sports drink on the trail?

Each format has a function. A fueling system only works if you understand what you are combining and why. Also read the article on energy bar vs. energy gel: when to use which for the full comparison.

Fruit performance bar. Solid fuel. The Eagle fruit performance bar delivers 20g of carbohydrates per 25g bar via the 2:1 glucose/fructose ratio. Vegan, gluten-free, lactose-free, 0% artificials. Not a gel, not a brick, not a snack. Soft texture: chewable at low to moderate intensity. On steep climbs or technical terrain where breathing peaks, switch to liquid sources.

Energy gel. Fast liquid carbohydrates. Gels typically provide 20g to 25g of carbohydrates per sachet and can be taken quickly without chewing. Combine each gel with at least 150-200ml of water. Without sufficient hydration, a hyperosmotic gel slows stomach emptying.

Sports drink. Carbohydrates and electrolytes at the same time. An isotonic sports drink (6-8% carbs) provides an average of 30g to 40g of carbohydrates per 500ml and simultaneously compensates for sodium and potassium loss through sweat. On warm trail days or during longer efforts, this is the link that connects hydration and fueling.

How do you build a concrete fueling plan for a 50K ultra?

A 50K ultra takes most trail runners four to seven hours. The target is 70g of carbohydrates per hour. You won't achieve this with a single format. The system works through combinations that you adjust to the intensity of the moment.

The basic logic: plan your intake at fixed intervals. Not by feel, not when you're hungry. Hunger on the trail is a late signal. If you feel it, you're already behind.

Hour 1 - build-up

For the first 30 minutes, your legs feel good. Glycogen stores are full. Still, you start fueling. Goal: 60g to 70g of carbohydrates in this hour. Workable combination: 1 Eagle fruit performance bar (20g) plus 500ml sports drink (35g) is 55g. Optionally add a gel at minute 45 if the pace is high to reach 70g.

Hour 2 and 3 - maintain

This is the crucial window. Glycogen reserves are decreasing. Goal: maintain 70g per hour. Combination per hour: 1 Eagle fruit performance bar (20g) plus 1 gel (22g) plus 250ml sports drink (18g) is 60g to 70g. Alternate based on intensity. On steep climbs: gel and drink. On flat sections or descents: fruit performance bar.

Hour 4 to finish - persevere

Stomach issues are more common in the second half of an ultra. Cumulative dehydration, reduced blood flow to the intestines, and high intensity inhibit gastric emptying. Stick to formats your body knows. Don't suddenly increase the volume. Maintain 60g to 70g per hour. The 2:1 glucose/fructose ratio in the Eagle fruit performance bar helps here: the split absorption via two transport channels reduces the strain on a single system and lowers the risk of stomach problems during prolonged exertion.

What mistakes do trail runners make most often regarding carbohydrate intake?

The most common mistake: starting too late. Trail runners who skip the first 45 minutes because they feel good build up a deficit that is difficult to compensate for later in the run. Taking carbohydrates when you are already empty is less efficient than proactive refueling.

The second mistake: relying on one format. Only gels on a seven-hour ultra is a recipe for flavor fatigue and mental resistance. Variation in texture—solid bar, liquid gel, drink—keeps the system workable. Read more about why athletes swap gels for a fruit performance bar.

The third mistake: too little water with gels. A hyperosmotic gel without water draws fluid into the intestine and can cause cramps. Combine each gel with at least 150ml to 200ml of water.

The fourth mistake: testing on race day. Every component of your fueling system should have been used during training. The gut trains along. A higher carbohydrate intake of 70g to 90g per hour is achievable but requires acclimatization over several weeks. Plan this twelve weeks before the race.

How does the Eagle fruit performance bar fit exactly into the 70g system?

An Eagle fruit performance bar weighs 25g and delivers 20g of carbohydrates with a carbohydrate density of 80g per 100g. Compact enough for a trail running vest. The 2:1 glucose/fructose ratio is built into the formulation, not added afterwards. 0% artificials, vegan, gluten-free, lactose-free. Certified Belgian production company (BRCGS Food Safety, ACS).

In a 70g per hour plan, one bar immediately adds 20g. Combine with a 22g gel and 250ml sports drink (20g to 25g), and you're at 62g to 67g. Add a second bar at a calm moment, and you reach 70g. Take the bar early in each hour: start of a climb, technical section at walking pace, checkpoint. Reserve the gel for moments when chewing is difficult.

The clean label aspect is not a marketing term here. On an ultra, you run for hours. Everything you ingest must be processed by your stomach under conditions of reduced blood flow and increased stress. Fewer unnecessary ingredients means fewer variables. Functional, not aesthetic. Compare labels yourself: fruit energy bar vs. ultra-processed sports nutrition.

How to train your gut for higher carbohydrate intake in trail running?

The gut is trainable. Regular carbohydrate intake during training increases the capacity of intestinal transport channels (SGLT1 and GLUT5). Specifically: start with 40g to 50g of carbohydrates per hour during long runs. Increase by 10g every one to two weeks. Trained athletes can reach 90g per hour without stomach problems.

Practical protocol for the twelve weeks before a 50K ultra:

• Week 1 to 4: 50g of carbohydrates per hour during every long run longer than 75 minutes. Use the Eagle fruit performance bar as a fixed component alongside sports drink.
• Week 5 to 8: Increase to 60g per hour. Add gel or extra sports drink as a second component.
• Week 9 to 12: Build up to 70g per hour. Test the exact combinations you will use on race day: bar, gel, drink, in the correct order.

Also train in the conditions you expect at the race: heat, altitude difference, technical terrain. A fueling system that works in flat conditions sometimes fails on a hot mountain trail. Test early, test often, adjust. Discover here why 70g+ is possible: read our main blog about carbohydrates.

What do you pack in your trail running vest for a 50K fueling plan?

A 50K race takes most athletes four to six hours. At 70g of carbohydrates per hour, you need 280g to 420g of carbohydrates. Considering checkpoints and carrying capacity:

• 4 to 6 Eagle fruit performance bars (80g to 120g carbohydrates)
• 4 to 6 energy gels (80g to 130g carbohydrates)
• 1.5 to 2 liters of sports drink spread throughout the race (90g to 160g carbohydrates)
• Supplementation via checkpoints depending on the course

Total: 250g to 410g of carbohydrates, matching a 70g per hour target over four to six hours. Six Eagle bars weigh 150g. Less than half a softflask. Compact, clean, functional. View the full range: Eagle fruit performance bars.

Fueling on the trail is the system that determines whether you reach the finish line in the condition you expect. Build it early. Test it thoroughly. Use formats you know and that your stomach accepts. During exertion. Period.

 

Choose your fuel