80 km Trail Running Nutrition: The Complete Guide to Optimizing Performance and Endurance

You're preparing to run your first 80 km trail race, or to improve your performance over this distance. Beyond the training plan and equipment choices, one question stands out: how to build a nutrition strategy that will truly support your effort for 8 to 15 hours?

Between your last pre-race meal and the finish line, your body must manage a massive energy deficit, progressive dehydration, and digestive constraints. How can you avoid hitting a wall at the 50 km mark and ensure you're among the finishers?

This guide provides concrete benchmarks, based on a scientific approach and standard recommendations in sports nutrition. It will help you prepare your nutrition for an 80 km trail race.

Why is nutrition essential for an 80 km trail race?

Energy needs during a long-distance trail race

During an 80 km trail race, total energy expenditure can reach several thousand calories, with high variability depending on the runner's profile, elevation gain, effort duration, and environmental conditions.

Nikolaidis et al. (2018) remind us in their review published in Nutrients that ultra-endurance events (lasting over 6 hours) frequently lead to significant caloric loss, which can exceed 7,000 kcal per day in some extreme cases.

However, the body only has 400 to 600 g of stored carbohydrates in the form of glycogen in muscles and the liver, which is less than 3,000 kcal available.

Your initial reserves are therefore insufficient to cover all your needs for such a long event. You must therefore compensate with regular carbohydrate intake.

Risks of a poor nutrition strategy

An unsuitable nutrition strategy exposes you to a progressive loss of energy, often experienced as a sudden drop in energy: heavy legs, dizziness, feeling unwell, loss of mental clarity, or even mental confusion.

As reserves are depleted, muscle fatigue sets in and reduces the muscles' ability to produce force: each stride becomes more difficult and your performance decreases.

Dehydration is another limiting factor. It can impair physical and cognitive abilities from approximately 2% body mass loss. However, excessive fluid intake can lead to hyponatremia (too low blood sodium levels).

Finally, gastrointestinal dysfunctions (nausea, reflux, diarrhea, vomiting or bloating) are among the problems frequently reported in ultra-endurance and can be a cause of abandonment or decreased performance (Costa et al., 2017).

The role of carbohydrates, fats, proteins, and electrolytes

In long-distance trail running, every nutrient plays a role.

Carbohydrates are the primary energy substrate during high-intensity phases. They fuel muscles and the central nervous system.

Fats can be used as the main energy source when intensity becomes moderate, but as soon as the pace quickens, carbohydrates become predominant again (Purdom et al., 2018).

Proteins primarily support muscle recovery. They can marginally contribute to energy production in extreme situations (very low glycogen reserves), but are not a priority fuel during exercise.

Electrolytes like sodium, play an essential role in fluid balance. They are useful in cases of heavy sweating, such as during an 80 km ultra-trail.

What to eat in the days before an 80 km trail race?

Optimizing glycogen reserves

A joint official position of the ACSM, the Academy of Nutrition and Dietetics, and Dietitians of Canada recommends gradually increasing your carbohydrate intake (8 to 12 g per kg of body weight per day) in the 48 to 72 hours leading up to the race. This carbohydrate loading phase helps optimize your glycogen stores.

Foods to prioritize

Opt for digestible starches like white rice, white pasta, white bread, semolina, or potatoes.

Compotes, ripe bananas, fruit juices, as well as honey or jam, also help to effectively increase carbohydrate intake.

In parallel, it is advisable to maintain a moderate protein intake, generally around 1.4 to 2.0 g/kg/day, in order to preserve your muscle mass (Jäger et al., 2017).

Foods to avoid before the race

In the 24 to 48 hours before an 80 km trail race, it is preferable to limit foods likely to increase the risk of digestive problems such as:

• fiber (raw vegetables, whole grains, legumes, whole fruits, etc.);
  
• fatty foods (fatty sauces, fried foods, cured meats);
  
• very spicy or heavily seasoned dishes;
  
• dairy products if you are sensitive to them;
  
• alcohol.
  

What to eat on race day before the start?

The ideal breakfast before a trail race

The meal you eat on the morning of the event has a simple goal: maximize carbohydrate availability to limit the risk of low blood sugar at the start of the effort. To prepare an appropriate breakfast, favor:

• digestible starches: white bread, rice pudding, semolina, rice cream;
  
• lean proteins: white ham, egg whites, cottage cheese;
  
• fruit: ripe banana or compote (apple, pear, peach, apricot, etc.).
  

Example of a classic breakfast before an 80 km trail race:

• 1 bowl of rice cream or semolina (prepared with water or plant-based milk);
  
• 1 to 2 slices of white bread + honey or jam;
  
• 1 compote (instead of a whole fruit);
  
• 1 yogurt or cottage cheese (if tolerated).

When to have your last meal before the start?

The optimal interval is generally between 3 and 4 hours before the start.

If the competition starts very early in the morning (e.g., 6 AM), it can be difficult to have a full meal at 2 or 3 AM.

In this case, prioritize a carbohydrate-rich dinner the night before, then a light snack 1 to 2 hours before the start (banana, compote, biscuits, or a small energy bar).

Hydration before the race

Drink regularly in the hours leading up to the start, in small sips, without excess. Clear to light yellow urine is often an indicator of proper hydration.

If you sweat a lot or if it's hot, opt for water containing electrolytes to arrive properly hydrated for your race.

What to eat during an 80 km trail race?

Energy needs during exertion

It is generally recommended to consume 30 to 60 g of carbohydrates per hour, or even up to 90 g/h for runners trained to tolerate this amount, particularly through sources combining glucose-fructose. These needs depend on each individual's profile and effort intensity. So, adjust your nutrition based on how you feel.

The best foods during a trail race

On the trail, some runners report that over the hours, salty foods become easier to tolerate than sweet products. That's why varying tastes and textures (sweet/salty, liquid/solid) often helps limit nausea.

Alternate between:

• gels, bars, fruit pastes, bananas, dates;
• chips, pretzels, sandwiches, salted potatoes;
  
• energy drinks containing glucose-fructose; even amino acids can be beneficial.

The importance of hydration and electrolytes

Even slight dehydration can increase perceived effort, accelerate fatigue, worsen digestive problems, and increase the risk of heatstroke.

Drink approximately 150 to 250 mL every 20 minutes and aim for a sodium intake of about 300 to 600 mg per hour. These values should be adapted to climatic conditions (heat, humidity), effort intensity, and your sweating profile.

How to manage aid stations

Never rely solely on official aid stations. Some stations may be empty, or the products offered may not match your dietary habits.

To carry with you:

• tested gels;
  
• salt or electrolyte tablets if necessary;
  
• a "backup" savory option (chips, mini sandwich).

Recommended strategy:

• use aid stations to restock;
  
• eat slowly while walking;
  
• avoid leaving with a full stomach.
  

How to avoid digestive problems during a trail race?

Testing your nutrition strategy during training

Thanks to gut training, you can improve your digestive tolerance by gradually accustoming your body to carbohydrate intake during exercise without discomfort (bloating, nausea, diarrhea).

Before the big day, test your nutrition strategy at least 3 to 5 times. Try the same products, quantities, and timing to limit unpleasant surprises during the race. Ideally, test your entire nutritional strategy during long training runs in preparation for the race!

Avoid irritating foods

Some foods or drinks may be less well tolerated during prolonged exertion, especially when intensity increases or digestion is reduced.

• fried foods and fatty sauces;
  
• foods rich in fiber (raw vegetables, legumes, whole grains);
  
• products with a high concentration of simple sugars or too hypertonic.

 Adapt your nutrition to intensity

On steep climbs or when your heart rate goes up, opt for liquids or semi-liquids (sports drink, gel, compote). Save solid foods for flat or downhill sections.

 

What to eat after an 80 km trail to optimize recovery?

Replenish energy reserves

Within 30 to 60 minutes after finishing the race, consume approximately 1 to 1.2 g of carbohydrates per kg of body weight to quickly restart glycogen resynthesis. You can start with a simple, easily digestible snack (recovery drink, smoothie, compote, white bread with honey), then follow up with a complete meal later.

Promote muscle recovery

A protein intake of approximately 20 to 40 g can be relevant at this stage (cottage cheese, eggs, chocolate milk, fish, chicken, or Whey if you use it) to support muscle repair.

Rehydrate the body

Rehydration should be gradual after exertion. A simple method is to weigh yourself before and after the race: for every kilogram lost, drink about 1.25 to 1.5 L in the following hours. To optimize fluid retention, adding sodium can be useful (salt, mineral-rich water, electrolyte drink). For this, you can use Hydratis tablets.

 

Example nutritional plan for an 80 km trail

Pre-race nutrition example

 In-race nutrition example

Post-race nutrition example

 

Common mistakes in 80km trail nutrition

Not eating enough

Due to digestive issues, some runners drastically limit their intake. Aim for at least 30 g of carbohydrates per hour, even if it seems like a lot.

Testing new foods on race day

Never test a product in competition. An unknown bar, a different gel, a new drink: to avoid risks of discomfort.

Neglecting hydration

Dehydration causes : decreased performance, digestive problems, risk of heatstroke. Drink regularly, even in cool weather.

Waiting until you're hungry or thirsty

The sensation of hunger and thirst comes too late. Eat and drink according to a regular schedule, regardless of your sensations. Set an alarm every 20 minutes if necessary.

 

FAQ: 80km trail nutrition

How much should you eat during an 80 km trail?

Aim for 30 to 60 g of carbohydrates per hour (or more depending on level and tolerance). Over 10 to 12 hours of effort, this represents 300 to 600 g in total.

What to eat during an ultra trail?

Vary between sweet foods (gels, bars, fruits) and savory foods (sandwich, chips, broth). Prioritize products tested during training. Solid foods can help diversify intake and improve tolerance over time.

How to avoid fatigue during a trail?

Eat regularly from the beginning without waiting until you're hungry. Maintain constant carbohydrate intake (30-50 g/h). Hydrate sufficiently. Test your nutritional strategy several times in training.

What foods should be prioritized during a trail?

Prioritize digestible carbohydrate sources: energy gels, bars, bananas, fruit pastes, sandwiches. Add savory foods in the second part of the race (chips, broth). Test everything in advance.

When to eat during a trail?

Start eating from the first hour. Break down your intake every 20 to 30 minutes rather than taking large quantities at once. Adapt to climbs (liquids) and flats (solids).

What drink to choose during a trail?

Choose an isotonic drink containing carbohydrates (6-8%) and sodium (~300 to 600 mg per hour). Alternate with pure water as needed. Test several brands to find the one that suits you.

 

Conclusion

Successful nutrition for an 80 km trail is neither random nor improvised. This ultra-endurance event requires a structured nutritional strategy.

Our recommendations are therefore: to optimize glycogen reserves before the race, to maintain approximately 30 to 60 g of carbohydrates per hour (or more depending on level and tolerance), and to continuously adapt hydration based on conditions and perspiration.

Test, adjust, repeat: this is the key to successful trail nutrition and optimized performance over 80 km.

 

Bibliography

Nikolaidis, P. T., Veniamakis, E., Rosemann, T., & Knechtle, B. (2018). Nutrition in Ultra-Endurance: State of the Art. Nutrients, 10(12), 1995. https://doi.org/10.3390/nu10121995

Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528. https://doi.org/10.1016/j.jand.2015.12.006

Jeukendrup A. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports medicine (Auckland, N.Z.), 44 Suppl 1(Suppl 1), S25–S33. https://doi.org/10.1007/s40279-014-0148-z

Sawka, M. N., Burke, L. M., Eichner, E. R., Maughan, R. J., Montain, S. J., & Stachenfeld, N. S. (2007). Amerige of Sports Medicine position stand: Exercise and fluid replacement. Medicine & Science in Sports & Exercise, 39(2), 377–390. https://doi.org/10.1249/mss.0b013e31802ca597

Costa, R. J. S., Snipe, R. M. J., Kitic, C. M., & Gibson, P. R. (2017). Systematic review: exercise-induced gastrointestinal syndrome-implications for health and intestinal disease. Alimentary pharmacology & therapeutics, 46(3), 246–265. https://doi.org/10.1111/apt.14157

Purdom, T., Kravitz, L., Dokladny, K., & Mermier, C. (2018). Understanding the factors that effect maximal fat oxidation. Journal of the International Society of Sports Nutrition, 15, 3. https://doi.org/10.1186/s12970-018-0207-1

Jäger, R., Kerksick, C. M., Campbell, B. I., Cribb, P. J., Wells, S. D., Skwiat, T. M., Purpura, M., Ziegenfuss, T. N., Ferrando, A. A., Arent, S. M., Smith-Ryan, A. E., Stout, J. R., Arciero, P. J., Ormsbee, M. J., Taylor, L. W., Wilborn, C. D., Kalman, D. S., Kreider, R. B., Willoughby, D. S., Hoffman, J. R., … Antonio, J. (2017). International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 14, 20. https://doi.org/10.1186/s12970-017-0177-8

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