The Ultimate Guide: How to Fuel for 100 Miles Like a Pro

October 9, 2025 •

4 min read

During an ultra-endurance event, your body can burn more than 10,000 calories, far more than you can replace during the race itself. Understanding how to fuel for 100 miles is therefore less about replacing every calorie and more about effectively managing your body's energy reserves.

Quick Summary

An in-depth ultra-endurance fueling strategy requires meticulous planning of pre-race carb-loading, continuous intake of carbohydrates and electrolytes during the event, and a disciplined post-race recovery protocol. Success depends on training your gut, practicing hydration, and having a variety of fuel sources to prevent palate fatigue and gastrointestinal issues.

Key Points

Pre-Race Carb-Loading: Maximize your glycogen stores by consuming 10-12g of carbohydrates per kg of body weight in the 24-48 hours before the race.
Consistent In-Race Fueling: Aim for 60-90g of carbohydrates per hour during the race to maintain energy levels and prevent bonking.
Stay Hydrated and Salty: Drink 500-1000ml of fluid per hour with added electrolytes, adjusting for conditions and sweat rate.
Mix Your Fuel Sources: Use a variety of gels, chews, and real foods to combat flavor fatigue and satisfy cravings during a long race.
Train Your Gut: Practice your exact race-day nutrition strategy during long training runs to ensure your stomach can handle it.
Recover Quickly: Consume a carb-to-protein snack within 30-60 minutes of finishing to kickstart muscle repair and glycogen replenishment.

The Foundation: Pre-Race Nutrition Strategy

Preparation is the cornerstone of any successful ultra-endurance event. Neglecting your nutrition in the days leading up to the race can sabotage your performance before you even start. This phase is about maximizing your body's energy reserves and ensuring you are fully hydrated.

Carb-Loading: Fueling the Tank

Carbohydrate loading is a crucial strategy for maximizing the glycogen stored in your muscles and liver. This provides a readily available fuel source for the duration of your race. A modern carb-loading protocol involves increasing your carbohydrate intake to 10-12 grams per kilogram of body weight over a 24-48 hour period leading up to the event. While doing this, it's wise to reduce your fat intake and choose low-fiber options to minimize the risk of gastrointestinal (GI) issues on race day. Good examples include white rice, pasta, potatoes, and sports drinks.

Race Day Breakfast: Topping Off Glycogen

Your glycogen stores will be slightly depleted overnight, so a substantial breakfast is necessary. Eat 2-4 hours before the race begins to allow for proper digestion. A meal rich in easily digestible carbohydrates with a small amount of protein is ideal. Examples include oatmeal with honey and bananas, or a bagel with a small amount of peanut butter.

Pre-Race Hydration

Start hydrating in the days leading up to the race by consistently drinking water. Your urine should be a pale yellow color, indicating adequate hydration. On race morning, drink 500-1000ml of fluid, which could include a sports drink with electrolytes, before the start.

In-Race Fueling: The Hour-by-Hour Plan

Once the race begins, consistent calorie and fluid intake is non-negotiable. Waiting until you feel hungry or thirsty is a recipe for disaster. The goal is to drip-feed your body with carbohydrates, fluids, and electrolytes to prevent bonking and dehydration.

Carbohydrate Intake: Steady Fuel Delivery

For ultra-endurance events, aim for a steady intake of 60-90 grams of carbohydrates per hour, depending on your intensity and body size. Using a combination of glucose and fructose, known as multiple transportable carbohydrates, can increase absorption rates and prevent stomach issues.

Here are some examples of what 60g of carbohydrates might look like:

2-3 standard energy gels (read labels)
~8 jelly babies or 3 mini bags of Haribo
1.5-2 packs of energy chews
1-2 bananas
A handful of salted pretzels and a sports drink

Hydration and Electrolytes: Preventing Imbalance

Sweating causes a loss of fluid and essential electrolytes, primarily sodium and potassium. Replacing these is crucial for maintaining muscle function and preventing cramping. Aim to consume between 500-1000ml of fluid per hour, with electrolytes added, adjusting for weather conditions and your personal sweat rate. Signs of an electrolyte imbalance include cramping and fatigue. Over-hydration (hyponatremia) is also a risk and can be serious.

Liquid vs. Solid Fuel: The Palate Fatigue Dilemma

Over the course of 100 miles, relying on a single type of fuel can lead to "palate fatigue," making it difficult to consume enough calories. Having a variety of textures and flavors is key to success.

Liquid Calories: Sports drinks and energy gels are easily absorbed and require minimal effort. They are great for maintaining a steady calorie intake, especially at higher intensities when digestion is compromised.
Solid Foods: Real foods, such as boiled and salted potatoes, rice cakes, and sandwiches, can provide a welcome change of pace. They are also useful for satisfying cravings for salt and savory flavors that often develop during long races.

Training Your Gut for the Big Day

Your digestive system needs training just like your muscles. Use your long training runs to practice your race-day nutrition plan, including the types of food and drinks, frequency, and amounts. This helps your gut become more efficient at absorbing fuel under stress and prevents race-day surprises.

Comparison of Fuel Sources


Fuel Source	Pros	Cons	Best Used For
Energy Gels	Quick energy boost, easy to carry, high carbohydrate content.	Can cause stomach distress, flavor fatigue, require water to wash down.	Short, intense efforts; for quick boosts late in the race.
Energy Chews	Easy to carry, provide measured doses of carbs, good for a steady drip.	Can be chewy and harder to eat when breathing is heavy.	Continuous fueling at a steady pace.
Real Food	Palate-cleansing variety, can be more satisfying psychologically.	Requires more digestion effort, can be bulky to carry, higher fiber/fat content.	Lower intensity periods, satisfying savory cravings.
Liquid Calories	Fast absorption, helps with hydration, less digestive effort.	Can be high in sugar, potentially leading to GI distress if too concentrated.	When appetite is low or at aid stations.

Post-Race Recovery: The Path to Rebuilding

After crossing the finish line, your body needs to begin the recovery process immediately. The initial 30-60 minutes post-race are critical for replenishing glycogen stores and repairing muscle damage. Aim for a carbohydrate-to-protein ratio of 3:1 or 4:1. A classic recovery choice is chocolate milk, while other options include a protein shake with a banana or yogurt with granola. Rehydrate with fluids and electrolytes, then follow up with a full, balanced meal within two hours. Rest and sleep are essential for a full recovery.

Conclusion: The Right Fuel Mix for 100 Miles

Successfully completing a 100-mile race depends heavily on a meticulously planned and practiced nutrition strategy. From deliberate carb-loading to consistent intra-race fueling and diligent post-race recovery, every stage is vital. The best approach is personalized, combining a mix of fuel sources to address both energy needs and palate fatigue. By respecting your body's signals and having a flexible plan, you can confidently tackle the immense challenge of an ultra-distance event. For more expert advice on preparing for endurance events, consider resources like Precision Hydration, which offers personalized fueling and hydration strategies.

Frequently Asked Questions

Most ultra-endurance athletes should aim to consume between 60 and 90 grams of carbohydrates per hour. The specific amount can depend on your body size and running intensity.

For carb-loading, focus on eating 10-12 grams of carbohydrates per kilogram of body weight per day in the 24-48 hours leading up to the race. Choose low-fiber, high-carb foods like white rice and pasta, and reduce fat intake.

Liquid fuels, such as sports drinks and gels, are easily digestible and provide quick energy. Solid foods, like rice cakes or potatoes, are digested more slowly but can help with palate fatigue and satisfy cravings for savory flavors during longer events.

Prevent bonking by fueling early and consistently with carbohydrates. Don't wait until you feel tired to start. Training your gut during practice runs and using a mix of glucose and fructose can also help maintain steady energy.

While individual needs vary, a general guideline is to drink 500-1000ml of fluid per hour. It's crucial to include electrolytes in your fluids, especially sodium, to replace what is lost through sweat.

Within 30-60 minutes post-race, consume a snack with a 3:1 or 4:1 ratio of carbohydrates to protein. Options like chocolate milk, a smoothie, or yogurt with fruit are effective for replenishing glycogen and aiding muscle repair.

Yes, testing your nutrition plan during long training runs is essential. This allows you to discover what foods and fluids your body tolerates well under stress and helps your digestive system adapt.

Yes, many ultra-runners incorporate real food. Easily digestible options include boiled and salted potatoes, white bread sandwiches, and rice cakes. However, practice with real food during training to ensure it doesn't cause GI distress.