What to Eat on a 100 Mile Ultra: Your Complete Fueling Guide

According to studies, 50–80% of ultra runners experience some form of gastrointestinal distress during races, highlighting the critical role of a well-executed fueling strategy. Knowing what to eat on a 100 mile ultra is a non-negotiable part of crossing the finish line successfully, often proving more challenging than the physical effort itself.

Quick Summary

This guide provides a strategic nutrition plan covering pre-race carb-loading, consistent in-race fueling, hydration and electrolyte management, and troubleshooting stomach issues for a 100-mile ultramarathon.

Key Points

• Pre-Race Carb-Loading: Maximize muscle glycogen stores by consuming 8–10 g of carbs/kg/day in the 48 hours before the race using low-fiber, familiar foods.

• Consistent In-Race Fueling: Aim for a steady intake of 60-90 grams of carbohydrates per hour, using a combination of sports products and real foods.

• Proactive Hydration: Drink 450-750 mL of fluid per hour, using electrolyte drinks or tablets to replace 300-700 mg of lost sodium.

• Combat Palate Fatigue: Rotate between sweet and savory foods, incorporating real food options like soup, potatoes, and sandwiches at aid stations.

• Manage GI Distress: If stomach issues arise, slow down your pace, switch to bland fluids, and focus on steady sips rather than large gulps.

• Train Your Gut: Practice your race-day fueling strategy extensively during training runs to improve digestive tolerance and find what works for you.

Why Ultra Nutrition is Your Fourth Discipline

For any athlete, completing a 100-mile ultramarathon is as much an eating contest as it is a running challenge. Your body’s internal glycogen stores can only power you for a few hours, meaning consistent carbohydrate intake throughout the race is essential to prevent 'bonking'. A solid fueling plan is the difference between a triumphant finish and a demoralizing DNF.

Pre-Race Fueling: The Foundation for Success

The work of fueling a 100-mile race begins long before the starting gun fires. By maximizing your glycogen reserves, you create the energy foundation for the epic journey ahead.

Carbohydrate Loading: The Final 48 Hours

In the 2-3 days leading up to the race, significantly increase your carbohydrate intake to saturate your muscles and liver with glycogen. Target an intake of 8–10 grams of carbohydrate per kilogram of body weight per day.

• Complex Carbohydrates: Focus on easily digestible sources like pasta, rice, bread, and potatoes.
• Avoid Experimenting: Stick to familiar, low-fiber foods you know your stomach tolerates well.
• Stay Hydrated: Steady hydration is crucial during this period; consider electrolytes alongside your water intake.

The Ideal Race-Morning Breakfast

About 2-3 hours before the race, eat a final carbohydrate-rich, low-fiber breakfast to top off your energy stores.

• Oatmeal: Simple and effective, with or without a little fruit.
• Toast or Bagel: With honey or jam for a quick sugar boost.
• Banana: An easily digestible source of carbohydrates and potassium.
• Small Amount of Protein: A little yogurt or a scrambled egg can be added, but keep it minimal to avoid digestive issues.

In-Race Strategy: The Core of the Challenge

Staying on top of your fueling during the race is a constant, proactive effort. Your mantra should be “Eat early, eat often”.

The Rocket Fuel: Consistent Carbohydrate Intake

Aim for a target of 60-90 grams of carbohydrates per hour, consuming small amounts frequently to maintain steady blood sugar.

• Energy Gels and Chews: These provide a quick, concentrated source of energy but require water for optimal absorption.
• Sports Drinks: A double-duty fuel source, delivering both carbohydrates and electrolytes. Many brands, like Tailwind or Skratch Labs, are popular among ultra runners.
• Dried Fruit: Dates and apricots offer natural sugar and are easy to carry.

Hydration and Electrolytes: Stay Balanced

Proper hydration is critical for performance and to prevent life-threatening conditions like hyponatremia.

• Fluid Intake: Sip 450-750 mL of fluid per hour, adjusting for weather and effort. Use a timer on your watch to remind you to drink consistently every 15-20 minutes.
• Electrolyte Replacement: Aim for 300-700 mg of sodium per hour, especially in hot conditions or if you are a heavy sweater. Salt tablets (such as SaltStick) and salty snacks are effective options.

The Buffet: When Real Food is a Lifesaver

In longer ultras, particularly after 6+ hours, palate fatigue can make sweet sports nutrition unappealing. This is when aid station real food becomes essential for both calories and morale.

• Savoury Options: Small portions of soup broth, boiled and salted potatoes, or pretzels.
• Comfort Foods: Peanut butter and jelly sandwiches (cut into small squares), or even a small slice of pizza or rice pudding in later stages.
• Fresh Fruit: Bananas and oranges are aid station staples, providing potassium and a fresh taste.

Comparison: Sports Nutrition vs. Real Food in Ultras

Knowing when to use each type of fuel can make or break your race.

Feature	Sports Nutrition (Gels, Chews)	Real Food (Sandwiches, Potatoes)
Energy Delivery	Fast absorption, quick energy boost.	Slower, more sustained energy; requires more digestion.
Convenience	Highly portable, easy to consume on the move.	Can be messy; often requires walking or aid station stop to eat.
Palatability	Limited flavor range; high sugar content can cause 'flavor fatigue'.	Wide variety of tastes and textures; helps curb cravings and boost morale.
Digestive Impact	Concentrated; can cause GI distress if not consumed with enough water.	Can be harder to digest during high-intensity effort; best for slower sections.

Troubleshooting Common Ultra Nutrition Issues

Even with a perfect plan, things can go wrong. Being prepared for common problems can save your race.

Managing Gastrointestinal Distress

If you experience nausea, bloating, or stomach cramps, it's often a sign of fueling overload or dehydration.

• Slow Down: Reduce your pace to allow your stomach to settle and improve digestion.
• Change Fuel: Switch to milder, easier-to-digest options like broth, crackers, or ginger ale.
• Reset: Stop all solid food intake for a period and focus on sipping fluids and electrolytes.

Palate Fatigue and Cravings

When the thought of another sweet gel makes you sick, it's time to get creative. This is a mental as much as a physical hurdle.

• Rotate Flavors: Alternate between different flavors and brands of sports nutrition to keep your taste buds interested.
• Listen to Cravings: A sudden desire for salty food may indicate a sodium deficit. Don't fight it—grab some pretzels or salty potatoes.
• Embrace Variety: The aid station buffet is your best friend. A bite of watermelon or a small piece of cheese can be a huge morale booster.

The Fourth Discipline: Training Your Gut

Your stomach can be trained just like your muscles. Use your long training runs to simulate race day fueling. Experiment with different foods, volumes, and timings to find what works best for you and your gut. Avoid trying any new foods or products on race day itself. This practice is vital for ensuring your system can handle the constant influx of calories and fluids under stress, making your race day fueling strategy a predictable strength rather than a point of failure.

Conclusion

Fueling a 100-mile ultra is an art and a science, requiring meticulous planning and consistent execution. By focusing on proper carb-loading, maintaining a steady intake of carbs and electrolytes during the race, and being prepared to adapt to mid-race challenges like stomach issues and palate fatigue, you can significantly increase your chances of success. Ultimately, the best nutrition strategy is the one you’ve practiced and refined over countless training miles, making it second nature when it matters most.

For additional resources on endurance fueling, consider exploring the guidance offered by sports nutrition experts like Precision Hydration (https://www.precisionhydration.com/performance-advice/nutrition/preparing-fueling-nutrition-plan-for-ultra-racing/).

Frequently Asked Questions

How many calories should I eat per hour during a 100 mile ultra?

Most runners aim for 250-350 calories per hour, with more experienced athletes pushing towards the upper end of that range, as supported by some studies.

Is it better to use gels or real food during an ultra?

The best approach is a combination of both. Gels and chews offer fast-absorbing energy, while real foods provide variety, more sustained energy, and a welcome mental break from sweetness, especially in the later stages of a long race.

How do I prevent 'bonking' in a 100-mile race?

Prevent bonking by fueling consistently from the start, aiming to consume carbohydrates every hour. You must start fueling before you feel hungry or low on energy, as your body's glycogen stores are limited.

What should I eat if I feel nauseous during the race?

If nausea strikes, slow down your pace, take a break from solid food, and switch to bland fluids like ginger ale or mild electrolyte drinks. Small sips of plain water can also help.

How important are electrolytes for a 100-mile ultra?

Electrolytes are crucial, especially sodium, for regulating fluid balance and preventing muscle cramps. Aim to consume 300-700mg of sodium per hour, using salt tablets, salty snacks, or sports drinks.

Should I try new foods during the race?

No, stick to the foods and products you have extensively tested during your training runs. Race day is not the time to experiment with new nutrition, which could lead to gastrointestinal issues.

Can I rely on aid stations for all my nutrition?

While aid stations offer a huge morale boost and plenty of options, you should not rely on them exclusively. Carry your preferred and tested nutrition with you, using aid stations for supplementary fuel and a change of pace.

What's a good way to practice my ultra nutrition plan?

Use your long training runs to simulate race day conditions. Practice consuming your planned fuel and hydration at your target pace and intensity to train your gut and identify any potential issues.