Nutrition and Hydration in Trail Running: What to Eat and Drink During an Ultra?

Ultras aren’t won by trained legs alone: they’re also won in the stomach and the hydration pack. For hours on end, the body burns hundreds of calories, loses liters of sweat, and must keep functioning. Without regular intake of energy and water, reserves deplete, blood sugar drops, and performance collapses. Conversely, poor nutrition can lead to nausea, digestive issues, or even chills. This guide explains why nutrition and hydration are trail running cornerstones, how much to consume, and how to organize your refueling strategy.

1. Why Nutrition and Hydration Are Essential

  • Maintain energy: endurance effort consumes huge amounts of calories. Without intake, the body draws from glycogen then fat reserves and quickly tires.
  • Ensure hydration and electrolyte balance: heavy sweating leads to water and salt loss. Regular intake of fluids and minerals prevents dehydration and cramps.
  • Prevent injuries and aid recovery: good nutrition reduces muscle breakdown and helps repair fibers during the effort.
  • Maintain stable weight and mental performance: regular intake prevents energy slumps and supports morale.

2. Determining Your Energy Needs

The body burns between 400 and 800 kcal per hour during an ultra. To avoid hitting the wall, aim for 200 to 400 kcal per hour from carbs, fats, and proteins. Rations vary with body size, intensity, and weather.

2.1 Carbohydrates

  • 20 to 50 km trails: 30 to 60 g of carbs per hour.
  • Ultra: 40 to 80 g/h.
  • Split intake every 30 to 45 min to stabilize blood sugar.
  • Vary textures (gels, drinks, bars, fruit purees, dried fruits) to avoid nausea.
  • Limit fiber and fat during the effort.

2.2 Proteins and Fats

  • For efforts over 8 hours: 10 to 15 g of protein per hour (protein bars, cheese, nuts).
  • Fats: 10 to 20 g/h in very long races to provide lasting calories – test during training.

2.3 Electrolytes

  • Recommended sodium: 500 to 700 mg/h.
  • Hydration: 500 to 1000 ml/h depending on temperature and intensity.
  • Isotonic drinks or electrolyte tablets make up for these losses.

3. Hydration: How Much and How?

  • Drink 500 to 750 ml per hour (up to 1 L/h in hot weather).
  • Don’t wait until you’re thirsty: drink every 10–15 minutes.
  • Use an isotonic drink (~30 g of carbs / 500 ml).
  • Adjust sugar concentration: more concentrated in cold weather, more diluted in heat.
  • Test your drink during training to ensure tolerance.

4. Choosing the Right Foods

4.1 Sweet

  • Gels, energy drinks, cereal bars, dried fruits.
  • Fruit or vegetable purees that are easy to swallow.
  • Jam, honey, or almond paste on white bread.

To prepare your race fueling, try different options on your long runs. You can also explore Pyrene Performance, a Trail Running Lab partner, and choose what suits your effort and digestion.

4.2 Savory

  • Broths, soups rich in sodium and fluids.
  • Chips, salty biscuits, crackers to balance the sweetness.
  • White bread sandwiches with cheese or ham.
  • Mashed potatoes or sweet potatoes.

4.3 Anti-nausea Tips

  • Alternate sweet and savory every 30–45 min.
  • Chew slowly to aid digestion.
  • Test all foods beforehand.

5. Refueling Strategy

5.1 Planning

  • Study the race profile to estimate needs.
  • Plan for 500 ml of drink per hour, adjust based on weather.
  • Distribute food in accessible pockets.
  • Use aid stations to refill, diversify food, and relax.

5.2 Adjust to Conditions

  • Heat/altitude: more hydration, electrolytes, easy-to-swallow foods.
  • Cold: solid and warm foods, broths, purees, thermos.
  • Duration: for >100 km, add fats (10–20 g/h) and proteins (10–15 g/h); for 50 km, focus on carbs.

5.3 Listen to Your Body

Adjust based on digestive tolerance and sensations: use purees or drinks if the stomach feels full, solid food if hungry.

6. Before and After the Race

6.1 Before

  • Meals rich in simple and complex carbs, low in fiber and fat.
  • Regular hydration and a salty drink the day before.
  • Prepare and test all nutrition gear.

6.2 After

  • Within 30 min: recovery drink (carbs + proteins).
  • Drink regularly to replace water and sodium losses.
  • Full meal with carbs and proteins within 2 hours, then regular snacks.
  • Enjoy food without overdoing alcohol.

Conclusion

Success in an ultra depends on fueling and hydrating the machine: plan your aid station strategy, consume 30–80 g of carbs per hour, add 10–15 g of protein and 10–20 g of fat in very long races, drink 500–1000 ml/h with 500–700 mg of sodium. Vary your foods, test during training, and stay flexible based on conditions and how you feel.