How do you fuel for an ultra marathon: A comprehensive guide

January 6, 2026 •

4 min read

Research shows that most ultra runners fail to meet their carbohydrate requirements during races, often consuming significantly less than the recommended 60-90 grams per hour, which directly compromises performance. Learning how to fuel for an ultra marathon properly is therefore one of the most critical aspects of race preparation and success.

Quick Summary

An effective ultra marathon fueling strategy encompasses pre-race glycogen supercompensation, consistent hourly carbohydrate and electrolyte intake during the race, and targeted post-race recovery nutrition. A successful plan requires training your gut, diversifying fuel sources to combat palate fatigue, and meticulous hydration planning based on individual sweat rates and conditions.

Key Points

Train Your Gut: Practice your race-day nutrition strategy during long training runs to help your stomach tolerate and properly absorb calories and fluids under stress.
Carb Load Effectively: For 48-72 hours pre-race, increase carbohydrate intake to maximize muscle glycogen stores, prioritizing easily digestible, lower-fiber foods.
Start Fueling Early and Often: Begin consuming 60-90 grams of carbohydrates per hour within the first 30 minutes of the race, taking in small amounts every 15-20 minutes.
Diversify Your Fuel Sources: Use a combination of gels, chews, liquid mixes, and real foods (like potatoes, sandwiches, or fruit) to combat palate fatigue during long events.
Prioritize Electrolyte Intake: In addition to fluid, ensure consistent intake of electrolytes, especially sodium, to prevent imbalances and dangerous conditions like hyponatremia.
Don't Forget Recovery: Immediately after finishing, consume a carb and protein mix to replenish glycogen and repair muscle tissue, followed by a balanced meal and continued hydration.

The Non-Negotiable: Training Your Gut

One of the biggest mistakes ultra runners make is under-fueling during the race, often due to gastrointestinal (GI) distress. To avoid this, you must train your gut to handle the caloric load you plan to consume on race day, just as you train your legs. Start practicing your race-day nutrition strategy during your long training runs, experimenting with different foods, drinks, and schedules to see what works best for your body. A trained gut will tolerate the stress of prolonged exercise and can properly absorb the necessary nutrients to keep you moving.

The Pre-Race Plan: Carb Loading for Peak Performance

Your ultra begins days before the starting gun with a proper carbohydrate-loading phase. For 48-72 hours prior to the event, increase your carbohydrate intake to saturate your muscle glycogen stores, which are your body's primary fuel source during endurance events. Aim for 8-10 grams of carbohydrates per kilogram of body weight per day during this time. Focus on easily digestible, lower-fiber carb sources like white rice, pasta, or bagels to minimize GI issues.

Breakfast (2-3 hours before): On race morning, have a familiar, carb-rich breakfast that you have tested during training. Good options include oatmeal with banana, toast with jam, or a plain bagel with honey.
Hydration: Start hydrating several days beforehand by consistently drinking water. In the hours before the race, have 400-600ml of fluid with electrolytes to top off fluid levels.
Electrolytes: Consider adding electrolytes to your water in the final days, as this can help with hydration and carb absorption.

The Race Day Strategy: Fueling on the Move

Consistent and regular fueling is key to avoiding 'the bonk,' or complete glycogen depletion. Your goal is to consume 60-90 grams of carbohydrates per hour, and potentially up to 120 grams per hour using a dual-carbohydrate source (glucose and fructose) for faster, more efficient absorption.

Liquid, Gel, and Solid Fuel Sources

Diversifying your fuel sources is crucial to combat palate fatigue, where you grow tired of the taste and texture of sweet products like gels over many hours. A mix of liquid, gels, and real foods works best.

Liquid Carbohydrates: Sports drink mixes offer dual benefits of hydration and easy-to-absorb calories. Brands like Tailwind and Skratch Labs provide a balanced approach.
Energy Gels and Chews: These provide a quick, concentrated hit of carbohydrates. Consume them in small amounts every 20-30 minutes rather than all at once to aid absorption and avoid GI issues.
Real Food: For longer events, real food provides satisfying calories and different tastes. Many ultra runners rely on options like mashed potatoes, bananas, pretzels, rice cakes, and savory snacks.

The Critical Role of Electrolytes and Hydration

Proper hydration and electrolyte balance are vital for performance and safety. Your needs are highly individual, but aim for 400-800ml of fluid per hour, adjusting for weather conditions and sweat rate.

Sodium: Replenish sodium lost in sweat with electrolyte products or salty foods. Recommendations typically range from 500-1000mg of sodium per liter of fluid, but this can vary significantly based on your sweat.
The Danger of Over-Hydrating: Drinking too much plain water can be dangerous, leading to hyponatremia (dangerously low blood sodium). A balanced hydration plan using electrolytes is key to avoiding this.

The Strategic Use of Caffeine

Caffeine is a powerful ergogenic aid that can reduce perceived exertion and delay fatigue. Save caffeinated products for later in the race, when you most need a mental and physical boost. It's crucial to experiment with timing and dosage during training to avoid adverse effects like GI issues or anxiety.

The Post-Race Recovery: Rebuild and Rehydrate

Nutrition doesn’t stop at the finish line. The hours and days following an ultra are crucial for recovery. Your body needs to replenish depleted glycogen stores, repair muscle tissue, and rehydrate.

The Anabolic Window: Within 30 minutes of finishing, consume a recovery snack or drink with a 3:1 or 4:1 carbohydrate-to-protein ratio. This helps kickstart the glycogen replenishment and muscle repair process. Chocolate milk is a classic example.
Balanced Meal: Within a few hours, have a larger, balanced meal with plenty of carbs, protein, and healthy fats. Listen to your body and its cravings for what it needs.
Continued Hydration: Continue to drink fluids and electrolytes to replace sweat losses and aid recovery.

Comparison of Ultra Marathon Fuel Types


Fuel Type	Pros	Cons	Best Used When
Energy Gels	Fast-acting carbs, portable, standardized dosage	Can cause stomach upset, taste fatigue, texture issues	Higher intensity sections, quick energy boosts
Energy Chews	Easy to chew, often with electrolytes/caffeine, portable	Can be sticky, may require more frequent intake	Consistent, mid-race calories
Liquid Mixes	Hydration and fuel combined, easy to consume	Can be difficult to manage multiple flavors/strengths	Hot conditions, consistent carb/electrolyte intake
Real Food	Palate variety, savory options, satisfying	Harder to carry, can be difficult to digest at high intensity	Slower, long-distance events, aid station fuel

Conclusion

Fueling for an ultra marathon is a complex, individual process that demands meticulous planning and consistent practice. By focusing on smart carbohydrate loading before the race, maintaining a steady intake of diverse fuel sources and electrolytes during the event, and prioritizing proper recovery nutrition, you can significantly enhance your performance and overall race experience. The golden rule is simple: never experiment on race day. Develop your strategy during training runs, listen to your body, and carry a variety of options to ensure you can meet the demands of the long haul. A successful finish often comes down to successful fueling. The International Society of Sports Nutrition provides excellent resources for developing an endurance nutrition plan for specific events and conditions.

Frequently Asked Questions

Most experts recommend consuming between 60 and 90 grams of carbohydrates per hour. Some advanced athletes can push this to 120 grams per hour, especially when using dual-carb sources like a glucose-fructose blend.

Start fueling early, within the first 30 minutes of the race. Do not wait until you feel hungry or low on energy, as it is difficult to catch up once your glycogen stores are significantly depleted.

Combat taste fatigue by diversifying your fuel sources. Rotate between sweet options like gels and chews with savory and real food options, such as pretzels, mashed potatoes, or broth, which aid in balancing your palate and appetite.

A general guideline is 400-800ml of fluid per hour, though this varies greatly based on individual sweat rate, weather, and intensity. Use thirst as a guide but also follow a pre-determined schedule, especially during very long events.

Salt tablets can be useful for replenishing sodium, especially for 'salty sweaters' or in hot conditions. However, many athletes meet their needs through electrolyte drinks and salty foods. Your individual sodium needs vary, so practice in training.

Within 30 minutes of finishing, consume a snack with a 3:1 or 4:1 carbohydrate-to-protein ratio. Chocolate milk, a recovery bar, or a smoothie are good options. Follow up with a balanced meal of carbs, protein, and healthy fats later.

Training with your race-day fuel is critical to teach your gut to handle absorption under stress and to identify any foods that cause GI issues. Failing to practice can lead to severe stomach problems and can end your race.