Fueling for the Long Haul: What to Eat During a 100 Mile Run

November 13, 2025 •

4 min read

According to the International Society of Sports Nutrition, a single-stage ultramarathon may induce an energy deficit of over 7,000 calories, underscoring the critical need for proper fueling. Understanding what to eat during a 100 mile run is the key to managing this massive energy expenditure, mitigating gastrointestinal distress, and sustaining peak performance for the long haul.

Quick Summary

A comprehensive guide on ultra-endurance fueling, detailing carbohydrate, protein, and fat intake strategies, hydration tactics, and food variety to manage palate fatigue during a 100-mile race.

Key Points

Train Your Gut: Practice your nutrition strategy on long training runs with the exact foods you'll eat on race day to build tolerance and avoid gastrointestinal issues.
Prioritize Carbohydrates: Aim for 30-60 grams of carbohydrates per hour, and potentially more with trained gut, using a mix of gels, chews, and real food.
Mix Food Types: Use both commercial sports products and real foods like salty potatoes, sandwiches, or soup to combat palate fatigue and provide a wider nutrient profile.
Balance Hydration and Electrolytes: Drink 450-750 ml of fluid per hour, adjusted for conditions, and include electrolytes (sodium) to replace sweat losses and prevent hyponatremia.
Start Fueling Early: Begin consuming calories and fluids within the first hour of the race, even if you don't feel hungry or thirsty, to stay ahead of the energy deficit.
Experiment with Variety: Keep a variety of flavors and textures in your drop bags to ensure you have palatable options when sweet gels lose their appeal.
Listen to Your Body: Learn to differentiate between true hunger/thirst and race fatigue, and adapt your plan based on how your body is responding to the demands of the race.

The Core Principles of Ultra-Distance Nutrition

Proper nutrition during a 100-mile run is a dynamic and personalized strategy, not a one-size-fits-all plan. Unlike shorter races, where reliance on glycogen stores is possible, ultramarathons require consistent, hourly intake of a variety of nutrients to prevent hitting the wall. The fundamental goal is to provide a steady supply of energy while training your gut to process fuel under physical stress.

Prioritizing Carbohydrates

Carbohydrates are the primary fuel for endurance exercise, and replenishing them consistently is non-negotiable. For ultrarunning, aiming for 30-60 grams of carbohydrates per hour is a standard starting point, though some athletes can tolerate up to 90g/hr by using multiple-transportable carbohydrate sources (e.g., glucose and fructose). This intake needs to begin early in the race, typically within the first hour, and continue like clockwork. Many runners find that a mix of sports nutrition products and real foods works best to meet this target and prevent palate fatigue.

Energy Gels and Chews: Provide a rapid and concentrated source of carbohydrates for quick energy boosts.
Sports Drinks: Combine fluid, electrolytes, and carbohydrates, making them a crucial component of your fueling strategy.
Energy Bars: Offer a mix of carbohydrates, protein, and fat, providing a more sustained energy release.

Incorporating Protein and Fat

While carbohydrates are king, protein and fat play increasingly important roles as the duration of the run extends. Studies suggest that protein intake during an ultra may help reduce muscle damage. Aiming for 5-10 grams of protein per hour can be beneficial, particularly in the later stages. Fat intake can also be effective during long-duration ultramarathons, with some successful finishers consuming higher amounts of fat compared to non-finishers. Incorporating small, tolerable amounts of fat can provide a calorie-dense energy source and help satisfy cravings for savory foods.

The Importance of Variety and Gut Training

Taste fatigue is a major factor in ultra-endurance racing, where the thought of another sweet gel can become unbearable. A successful strategy involves rotating between sweet and savory options. This is where aid stations and drop bags become your best friend, offering a variety of flavors and textures to keep your stomach happy. Foods like salty potatoes, chips, and broth-based soups are common choices for resetting the palate. The key to integrating these diverse foods is practicing with them during long training runs to ensure your gut can tolerate them under stress. Your gut can be trained just like your legs, so don't wait for race day to experiment.

Hydration and Electrolyte Strategy

Staying hydrated is paramount and intrinsically linked to nutrient absorption. The American College of Sports Medicine recommends 450-750 ml of fluid per hour, with 500-700mg of sodium per liter, especially in hot conditions. However, this is a guideline, and individual needs vary significantly based on sweat rate, climate, and pace. Over-hydration can lead to hyponatremia, a dangerous condition caused by low blood sodium, while dehydration impairs performance. Monitoring urine color, thirst, and body weight changes during training can help fine-tune your hydration plan. Using electrolyte tablets or electrolyte-enhanced drinks is an excellent way to balance fluid intake with sodium replacement.

Comparison of Fuel Types


Feature	Energy Gels/Chews	Real Food (e.g., Bananas, Wraps)	Liquid Nutrition (e.g., Sports Drink, Soup)
Carbohydrate Source	Concentrated, fast-acting sugars	Natural sugars, complex carbs	Multiple-transportable carbs, glucose
Digestion Speed	Very fast; easy absorption	Slower; requires more gut work	Very fast; bypasses solid food digestion
Taste Fatigue	High risk; can be overly sweet	Low risk; provides variety	Moderate risk; can be monotonous
Nutrient Density	High in carbs, low in other nutrients	Balanced; includes vitamins and minerals	Good for electrolytes and fluids
GI Distress Risk	Moderate; depends on personal tolerance	Lower; familiar foods are easier to digest	Low; especially when appetite is poor
Practicality	Lightweight, easy to carry and consume	Requires preparation and carrying capacity	Convenient via hydration pack or bottles

Conclusion

Successfully completing a 100-mile run is a physical and mental challenge where nutrition is a major determinant of success. The process of discovering what to eat during a 100 mile run begins long before race day, requiring diligent practice and self-awareness during training. A varied approach incorporating commercial sports nutrition products, calorie-dense whole foods, and liquid calories is most effective in combating palate fatigue and maintaining consistent energy intake. A solid hydration and electrolyte strategy, fine-tuned in training, is equally crucial for avoiding performance-hindering conditions like dehydration and hyponatremia. Remember, listen to your body, train your gut, and be prepared to adapt your fueling plan to the ever-changing demands of a long race. For additional resources on developing an ultrarunning plan, explore guides from reputable sources, like the advice from Sports Dietitians Australia.

Frequently Asked Questions

Most ultrarunners aim for 200-400 calories per hour, with a primary focus on easy-to-digest carbohydrates. This can be achieved through a mix of energy gels, sports drinks, and solid foods.

Yes, it is highly recommended to eat solid food during an ultramarathon to avoid palate fatigue and provide a more balanced nutrient intake. Many runners rely on aid stations for foods like salty potatoes, sandwiches, and soup.

Bonking is a state of severe fatigue caused by the depletion of your body's glycogen stores. Consuming carbohydrates consistently throughout the race, typically 30-60g per hour, helps to prevent this by providing a steady energy source.

Preventing GI issues involves consistent gut training during practice runs, avoiding unfamiliar foods on race day, and choosing easily digestible, low-fiber carbohydrate sources during the race. Liquid calories can also be helpful when your stomach is upset.

Electrolytes, particularly sodium, are crucial for maintaining proper hydration and nerve function. Replacing lost electrolytes, especially in hot conditions, is key to preventing conditions like hyponatremia and muscle cramping.

A combination of both is often best. Sports nutrition products offer concentrated, easy-to-carry carbs, while real foods like bananas, potatoes, and soup provide variety and a broader spectrum of nutrients to combat taste fatigue.

If you experience appetite loss, focus on liquid calories and easily digestible, non-sweet foods. Broth-based soups, sports drinks, and salted potatoes are often tolerable and provide essential calories and electrolytes.