Ultramarathon Nutrition Strategy: A Comprehensive Fueling Plan from Training to Race Day

An ultramarathon (Ultra Marathon) generally refers to any running event longer than 42.195 kilometers, ranging from 50K to 100 miles or even farther. At such distances, physical fitness is no longer the sole determining factor—your nutrition and fueling strategy often dictates whether you can finish, and the quality of that finish. According to research, gastrointestinal issues rank among the top three reasons for DNF (Did Not Finish) in ultramarathons. This article delves into every aspect of ultramarathon nutrition.

The Truth About Ultramarathon Energy Expenditure

Basic Energetics

The average runner expends approximately 1 kcal / kg body weight per kilometer, but ultramarathons involve climbs, varied terrain, and prolonged inefficient running, resulting in higher actual expenditure:

Race Type	Estimated Total Expenditure (70kg Runner)	Duration
50K Road Ultramarathon	3,500-4,000 kcal	4-6 hours
100K Trail Ultramarathon	8,000-10,000 kcal	10-16 hours
100 Mile Trail Ultramarathon	12,000-18,000 kcal	20-36 hours

The human body stores approximately 1,600-2,000 kcal of glycogen, and even with carb-loading strategies, this can only be maximized to about 2,500 kcal. This means ultramarathon runners must continuously replenish energy during the race, or they will inevitably hit the wall.

The Role of Fat Oxidation

The good news is that trained endurance athletes possess remarkably high fat oxidation capacity at low intensities. Proponents of the MAF (Maximum Aerobic Function) training method advocate training the body to use fat as its primary fuel source, thereby reducing reliance on exogenous carbohydrates.

However, the latest sports nutrition research (including the 2024 ISSN position statement) points out: even athletes who are well fat-adapted still need to continuously supplement carbohydrates during ultramarathon events. The upper limit of fat oxidation rate is approximately 1.0-1.5 g/kg per hour, which cannot fully cover the energy demands of moderate-to-high intensity exercise.

Pre-Race Nutrition Preparation

Carbohydrate Loading

Perform carbohydrate loading 2-3 days before the race, with the goal of maximizing glycogen stores:

Daily Carbohydrate Intake Target: 8-12 g/kg body weight

For a 70kg runner as an example, this means 560-840 grams of carbohydrates per day. This requires deliberate dietary planning:

High-Carbohydrate Food List:

• One bowl of white rice (approx. 200g): approximately 70g carbs
• One serving of pasta (100g dry weight): approximately 75g carbs
• Sweet potato 300g: approximately 60g carbs
• One banana: approximately 27g carbs
• Sports drink 500ml: approximately 30g carbs

Important Notes:

• Avoid high-fiber foods (which can cause gastrointestinal discomfort)
• Reduce fat intake (to free up “stomach space” for carbohydrates)
• Don’t overeat at dinner the night before the race, as it may affect sleep quality

The Final Pre-Race Meal

Eat your last full meal 3-4 hours before the start:

• Carbohydrate-focused: white rice, white toast, congee
• Small amount of protein: boiled eggs, chicken breast
• Avoid: dairy products, high-fiber vegetables, spicy foods, caffeine (save it for during the race)

15-30 minutes before the start, you can take one energy gel or a few sips of sports drink.

In-Race Fueling Strategy

Carbohydrate Intake Targets

This is the most critical number in ultramarathon nutrition. Based on the latest research recommendations:

Race Duration	Hourly Carbohydrate Target	Notes
4-6 hours	60-80g	Primarily glucose + fructose mixed sources
6-12 hours	60-90g	Requires solid food supplementation
12+ hours	50-80g	Digestive capacity declines, requiring more flexible adjustments

Key Concept: Multiple Transportable Carbohydrates

The small intestine’s absorption rate limit for glucose is approximately 60g per hour (via the SGLT1 transporter). By adding fructose, additional absorption can occur through the GLUT5 transporter, increasing total carbohydrate absorption to 90-120g/hour.

Therefore, choosing products containing glucose (or maltodextrin) + fructose is more efficient than a single carbohydrate source. The optimal ratio is approximately glucose:fructose = 1:0.8.

Fuel Product Selection and Combination

Liquid Fuel (Fast Absorption):

• Sports drinks: 6-8% carbohydrate concentration, easily absorbed
• Energy gels + water: approximately 20-25g carbs per packet, one every 30-45 minutes
• Cola (flat): caffeine + sugar, the “miracle drug” for the latter half of an ultramarathon

Semi-Solid Fuel (Medium Absorption):

• Energy fruit jellies: texture between gel and solid, gentle on the stomach
• Baby food purees: inexpensive, easy to swallow, variety of flavors

Solid Fuel (Slow Absorption, Provides Satiety):

• Rice balls (salted): a classic Taiwanese ultramarathon staple
• Boiled potatoes with salt: common in Western ultramarathons, high GI and contains potassium
• Pretzels: a carbohydrate + sodium combination
• Fruits: bananas, watermelon, oranges

Electrolyte Management

Prolonged sweating causes significant electrolyte loss, particularly sodium. Hyponatremia is one of the most dangerous medical conditions in ultramarathons.

Sodium Supplementation Recommendations:

• 500-1000mg sodium per hour (adjust based on sweat rate and temperature)
• Use electrolyte capsules (such as SaltStick, Precision Hydration)
• Add salt to food: salted rice balls, potato chips, miso soup

Fluid Intake:

• 400-800ml per hour, adjusted according to thirst level
• Do not overhydrate: drinking too much plain water dilutes blood sodium concentration
• Use body weight as a monitoring indicator: a 2-3% weight loss during the race is normal

Caffeine Strategy

Caffeine is a legal performance enhancer, especially important for ultramarathon runners:

• Delay usage: Save caffeine for the latter half of the race (typically after the halfway point)
• Dosage: 3-6mg per kg body weight, taken in divided doses
• Sources: caffeinated energy gels, cola, caffeine tablets
• Caution: If you don’t regularly drink coffee, test caffeine’s effect on your stomach during training first

Gut Adaptation Training

This is the critical training that most runners overlook. Your digestive system needs to be trained just like your legs.

Training Principles

1. Practice fueling during long training runs: Every long run is an opportunity to test fueling products
2. Gradually increase intake: Start at 40g carbs per hour, increase by 10g every 2-3 weeks
3. Simulate race conditions: Test fueling strategies at your target pace and intensity
4. Record gastrointestinal responses: Note which foods work and which cause discomfort, building a personal database

Common Gastrointestinal Issues and Solutions

Symptom	Possible Cause	Solution
Nausea	Carbohydrate concentration too high	Dilute drinks, switch to low-osmolality products
Bloating	Intake rate too fast	Smaller, more frequent intake, avoid carbonated drinks
Diarrhea	High fiber or dairy products	Low-residue diet 24 hours before the race
Vomiting	Dehydration or excessive intake	Pause solid foods, take small sips

Post-Race Recovery Nutrition

0-2 Hours After Finishing (Golden Recovery Window)

• Carbohydrate to protein ratio of 3:1 to 4:1
• Target: 1-1.2g/kg carbs + 0.3g/kg protein
• Easily digestible foods: chocolate milk, recovery drinks, white rice with chicken

24-72 Hours After Finishing

• Increase protein intake to 1.6-2.0g/kg per day to promote muscle repair
• Anti-inflammatory foods: deep-sea fish, blueberries, turmeric
• Adequate hydration: until urine returns to a light yellow color

Conclusion

Ultramarathon fueling is not something you start thinking about on race day—it needs to be systematically practiced and tested during training. Remember this famous saying from the ultramarathon world: “Nothing new on race day.” Every food, drink, and fuel product you use during the race should have been repeatedly validated in training. Treat your gut as another muscle that needs training; its performance will directly determine your ultramarathon results.

Related Reading

• Ultramarathon Diet Strategy: Energy Fueling Plan for 24-Hour Races
• Ultramarathon Fueling Strategy: Solid Food vs. Liquid Fuel Ratios for 100km Races
• Ultramarathon Fueling Strategy: Energy and Electrolyte Rhythm from 50K to 100K
• Complete 100K Ultramarathon Fueling Rhythm Plan: The Scientific Formula for Hourly Calories, Sodium, and Solid-Liquid Transitions