Ultramarathon Fueling Strategy: How to Actually Eat 60-90g of Carbs Per Hour Without Wrecking Your Stomach?

Why 60-90g of Carbs?

The maximum carbohydrate absorption rate during exercise:

• Glucose only: 60g/hour (limited by the SGLT-1 transporter in the small intestine)
• Glucose + Fructose blend (2:1): Up to 90-100g/hour (fructose uses a different pathway via GLUT-5)

Ultramarathons last 8-24 hours, and glycogen is depleted at 60-80g per hour—if fueling falls behind, you hit the wall.

Fueling Timeline Breakdown (Using a 12-Hour 100K as an Example)

Fueling Food Calorie Comparison

Energy Gels

Solid Foods

Liquid Fueling

Why Does Your Stomach Blow Up?

Causes of gastrointestinal issues:

1. Carb concentration too high: Osmolality above 8% slows gastric emptying
2. Excess fructose: Large amounts of fructose alone can cause diarrhea
3. Heat and dehydration: Dehydration reduces gastric blood flow, causing food to linger
4. Getting sick of the same fuel: Taste fatigue affects eating
5. Nervousness: Stress raises cortisol, slowing gastric emptying

Strategies to Prevent Stomach Blowout

Strategy 1: Variety

• Switch fuel every 30 minutes (sweet → savory → liquid → solid)
• Prepare a “savory backup plan” before the race: miso soup, potato chips, savory congee

Strategy 2: Liquid First

• After 8 hours, switch to Maurten or Tailwind as the primary fuel
• Reduce solid food to 20-30%

Strategy 3: Small Bites

• Don’t eat an entire energy bar at once
• Cut it into small pieces and take a bite every 5-10 minutes

Strategy 4: Match Water Intake

• For every 1g of carbs, pair it with 8-10ml of water
• 90g carbs/hour ≈ 800ml of water

Electrolyte Fueling

Not enough carbs and you hit the wall; not enough electrolytes and you get cramps, nausea, and weakness.

Common Ways to Supplement

• Salt tablets (e.g., SaltStick) 1-2 per hour
• Electrolyte powder mixed in water (Skratch, LMNT)
• Savory foods (pickled plums, salted potatoes, saltine crackers)

Fueling Adjustments for Hot Weather

When temperatures exceed 28°C:

• Appetite for solid food drops, increase liquid ratio to 70%
• Increase sodium intake by 20-30%
• Add ice or cold drinks to cool down
• Avoid high-fat foods (such as peanut butter)

6-Week Pre-Race Gut Training

“Training your gut” is an often-overlooked part of ultramarathon training:

• Simulate race-day fueling rhythm during long runs
• Gradually increase from 40g per hour to 80g
• Test your tolerance for various foods
• No new foods within 2 weeks before the race

Common Mistakes

1. Only eating gels: You’ll absolutely get sick of them after 3 hours, and your stomach will rebel
2. Not practicing eating: If you don’t fuel during training, your gut goes on strike during the race
3. Eating too late: Once you feel hungry, it’s already too late
4. Not drinking water: Taking gels without water makes gastric juices thick and triggers nausea

Conclusion

Ultramarathon fueling is the art of “consistent, varied, and moderate.” The 60-90g of carbs per hour is the scientific ceiling, but whether you can actually get it down depends on long-term gut training. Race day is not the place to test new strategies.

Related Reading

• Ultramarathon Fueling Calculator: Personalizing Hourly Carb Grams and Fluid Intake
• Ultramarathon Fueling Strategy: Energy and Electrolyte Rhythm from 50K to 100K
• Training Fueling Strategy: How to Achieve 60–90g of Carbs Per Hour
• Ultramarathon Pre-Race Carb Loading: How to Properly Execute 48-Hour Carb Supercompensation