Running more than 50 km, often in the mountains, for 6 to 30 hours: ultra-endurance imposes unique metabolic constraints. Nutrition isn't a logistical detail — it's the 4th pillar of performance, after training, recovery, and mental toughness. Here's what science recommends in 2026.

🎯 Preparing for an ultra-trail or marathon?

Our physical preparation team supports you in optimizing your nutrition and training.

Discover Physical Preparation

The Metabolic Challenges of Ultra-Endurance

An ultra-trail runner burns between 300 and 600 kcal per hour, creating a potential caloric deficit of 5,000 to 15,000 kcal over a race. The problem: the stomach can only absorb a fraction of this energy. Managing this imbalance is at the heart of the nutritional strategy.

60-90g/h

Recommended race carbohydrates

450-750 mL/h

Target hydration

500-1000 mg/h

Sodium in hot conditions

Training Carbohydrates: The Energy Foundation

The ISSN's official position is clear: ultra runners should consume 5 to 8 g of carbohydrates per kg of body weight per day during training. For a 70 kg athlete, that's 350 to 560 g of daily carbohydrates.

Recommended macronutrient distribution: approximately 60% carbohydrates, 15% protein, 25% fat. This ratio ensures optimal glycogen replenishment between sessions while supporting muscle recovery.

📋 Nutritional Periodization

The "train low" trend (training with low glycogen stores) may stimulate certain mitochondrial adaptations. However, the ISSN warns: this strategy compromises performance during high-intensity sessions and increases injury risk. Use sparingly, never as a default.

  • • Long/easy sessions: moderate carbohydrate intake acceptable
  • • Intensive sessions (threshold, VO2max): always well-fueled
  • • Race week: glycogen supercompensation 48-72h before

Race Nutrition: The Key Protocol

This is where races are won or lost. The goal is to consume 150 to 400 kcal per hour, primarily as carbohydrates (30-50 g/h minimum, ideally 60-90 g/h) and protein (5-10 g/h).

⚡ Multiple Transportable Carbohydrate Ratio

To exceed the 60 g/h barrier, you must combine glucose + fructose (2:1 or 1:0.8 ratio). Glucose uses the SGLT1 transporter, fructose uses GLUT5 — two distinct absorption pathways allowing a higher total intake.

  • • <60 g/h: glucose alone suffices
  • • 60-90 g/h: glucose:fructose 2:1 ratio required
  • • 90-120 g/h: possible with specific gut training

Race-Day Protein: An Underestimated Need

Contrary to popular belief, protein plays a role during ultra races. Beyond 4-6 hours of effort, muscle catabolism intensifies. An intake of 5-10 g of protein per hour helps limit muscle breakdown and improves food palatability — a crucial factor when nausea sets in.

In practice: alternate between sweet (gels, drinks) and savory sources (cheese, ham, broth). Studies show an increasing preference for savory foods beyond 6 hours of racing.

Hydration: Not Too Much, Not Too Little

Dehydration impairs performance, but overhydration (hyponatremia) can be fatal. ISSN recommendations suggest 450-750 mL per hour, adjusted for heat, altitude, and individual sweat rate.

💧 Practical Hydration Strategy

  • • Weight loss ≤2%: tolerable without significant performance impact
  • • Weight loss >3%: measurable performance decline, increased injury risk
  • • Weight gain during race: hyponatremia danger — reduce fluid intake immediately
  • • Weigh before/after training: the best tool to calibrate your hydration plan

Sodium & Electrolytes: The Forgotten Factor

Sodium is the most critical electrolyte in ultra. Sweat losses range from 300 to 2,000 mg of sodium per liter of sweat depending on the individual. In hot conditions or during prolonged efforts, an intake of 500-1,000 mg of sodium per hour is recommended.

Gastrointestinal Issues: The #1 DNF Factor

Up to 85% of ultra-runners report gastrointestinal issues (nausea, vomiting, diarrhea, bloating). This is the leading cause of DNFs and underperformance. Prevention:

🛡️ GI Issue Prevention

  • • Train the gut: practice your nutrition during training, not just on race day
  • • Avoid fiber and fat: in the 3-4h before the race and during effort
  • • Split your intake: small frequent amounts rather than large meals at aid stations
  • • Drink temperature: cool (not ice-cold) beverages are better tolerated
  • • No NSAIDs: ibuprofen increases intestinal permeability 3x during exercise

Evidence-Based Supplementation

✅ Caffeine

3-6 mg/kg, divided during the race. Improves alertness and delays perceived fatigue.

✅ Creatine

3-5 g/day during training. Improves recovery and muscle strength.

✅ Beetroot juice (nitrates)

300-600 mg nitrates. Improves running economy by 1-3% via better mitochondrial efficiency.

✅ Vitamin D

1000-4000 IU/day if confirmed deficiency. Crucial for bone health and immune function.

Post-Race Nutritional Recovery

  • • 0-30 min post-race: 1-1.5 g/kg carbohydrates + 0.3 g/kg protein
  • • 1-4h post-race: full meal rich in carbohydrates, protein and natural antioxidants
  • • 24-72h post-race: high protein intake (1.6-2.2 g/kg/day) for muscle repair
  • • Rehydration: 150% of weight lost in fluids within 4-6h

Practical Nutrition Plan: 100 km Example

📋 Nutrition Timeline

D-3 to D-1: Glycogen Loading

8-12 g/kg/day of carbohydrates. Reduce fiber. Optimal hydration.

Race Day, 3h Before Start

Familiar meal: 2-4 g/kg carbohydrates (white bread, jam, banana). Avoid fat and fiber.

Km 0-40: Building Phase

60-80 g/h carbohydrates (gels, drinks). 500 mL/h. Mostly sweet sources.

Km 40-70: Transition Phase

Alternate sweet/savory. Add solid protein (cheese, ham). 40-60 g/h carbohydrates.

Km 70-100: Survival Phase

Eat whatever works. Salted broth, Coca-Cola, small bites. Maintain hydration.

Frequently Asked Questions

How many carbohydrates per hour in ultra-trail?

The ISSN recommends 30-50 g/h minimum, ideally 60-90 g/h with a 2:1 glucose:fructose mix. Beyond 90 g/h, specific gut training is necessary.

Is the ketogenic diet suitable for ultra?

Fat adaptation may help at low intensity, but science shows reduced performance at high intensity and a higher energy cost of lipid oxidation. The ISSN recommends a high-carbohydrate diet.

How to prevent nausea during racing?

Train the gut by repeating your nutrition strategy during training. Split intake. Avoid fiber, fat and NSAIDs. Prefer cool drinks and alternate sweet/savory after 6h of effort.

Is sodium really necessary during racing?

Yes, especially beyond 4h or in hot conditions. Sweat sodium losses range from 300-2,000 mg/L. An intake of 500-1,000 mg/h is recommended to prevent hyponatremia and cramps.

Should I take caffeine during ultra?

Yes, caffeine (3-6 mg/kg) improves alertness and delays fatigue. Split the dose (e.g. 50-100 mg every 2-3h) rather than a single dose. Test your tolerance in training.

Sources

  • • Tiller NB et al. (2019). ISSN Position Stand: Nutritional Considerations for Single-Stage Ultra-Marathon Training and Racing. Journal of the International Society of Sports Nutrition, 16(1):50.
  • • Jeukendrup AE (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Medicine, 44(Suppl 1):25-33.
  • • Costa RJS et al. (2017). Systematic review: Exercise-induced gastrointestinal syndrome. Alimentary Pharmacology & Therapeutics, 46(3):246-265.
  • • Hoffman MD & Stuempfle KJ (2015). Sodium supplementation and exercise-associated hyponatremia during prolonged exercise. Medicine & Science in Sports & Exercise, 47(9):1781-1787.
  • • Stellingwerff T & Cox GR (2014). Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying duration. Applied Physiology, Nutrition, and Metabolism, 39(9):998-1011.

🏔️ Ready to optimize your ultra nutrition?

Our physical preparation team supports you in planning your next ultra-trail: training, nutrition, and race strategy.

Book a Consultation