How to Properly Refuel During Long Runs? Your Complete Guide

November 10, 2025 •

5 min read

Studies show that up to 96% of endurance athletes experience some form of gastrointestinal issue during long-distance events. Learning how to properly refuel during long runs is crucial not just for performance, but also for comfort and gut health.

Quick Summary

A comprehensive guide on strategic fueling during long runs. It details carbohydrate and electrolyte needs, compares different fuel types like gels and real food, and provides a structured approach to gut training to avoid gastrointestinal issues and optimize performance.

Key Points

Strategic Fueling Timing: Start consuming 30-90g of carbohydrates per hour within the first 60 minutes of runs lasting over 90 minutes, taking small, frequent doses.
Hydrate with Electrolytes: Don't just drink water; replenish sodium and other electrolytes lost through sweat to prevent dehydration and hyponatremia.
Train Your Gut: Systematically practice your race-day fueling plan during training runs to improve your digestive system's tolerance for on-the-run nutrition.
Practice Makes Perfect: Never introduce new fuels, hydration strategies, or timings on race day. Stick with what you've rehearsed in training.
Optimize Recovery: Consume a 3:1 or 4:1 carbohydrate-to-protein snack within 30-60 minutes post-run to kickstart glycogen replenishment and muscle repair.
Personalize Your Approach: Every runner's body is different. What works for one person may not work for another, so consistent experimentation is key.

The Fundamentals of Mid-Run Fueling

For any run lasting longer than 60 to 90 minutes, your body's stored muscle glycogen starts to deplete, leading to a loss of energy often called "hitting the wall". To sustain your effort, you must supplement your body's energy reserves from the very start of the run. Your goal is to provide a consistent, easily digestible source of carbohydrates to keep your engine running smoothly.

Why Your Body Needs Fuel

Your muscles rely on glycogen for high-intensity, prolonged exercise. The longer and harder you run, the more you burn through these limited stores. Without consistent intake of carbohydrates, your body is forced to rely on fat for fuel, a less efficient process that can lead to a significant drop in performance. By providing carbohydrates throughout your run, you help spare your glycogen stores, maintain blood sugar levels, and reduce fatigue.

The Hourly Carbohydrate Target

Research has shown that endurance athletes should aim to consume between 30 and 90 grams of carbohydrates per hour for activities over 90 minutes. For marathons and ultra-marathons, aiming for the higher end of this range (60-90g/hr) is often recommended. Many modern sports nutrition products use a combination of glucose and fructose, which allows for greater absorption by the gut and can reduce the risk of gastrointestinal (GI) issues compared to products with just one type of sugar.

Hydration and Electrolytes

Fueling isn't just about calories; it's also about fluids and electrolytes. Dehydration can lead to a host of problems, including reduced performance and GI distress. Over-hydration with plain water can be equally dangerous, potentially causing hyponatremia (dangerously low blood sodium levels).

Key Hydration Rules:

Drink regularly: Sip fluids consistently throughout your run, approximately every 15-25 minutes. Don't wait until you feel thirsty, as thirst is already a sign of dehydration.
Include electrolytes: Consume electrolytes, particularly sodium, to replace what you lose through sweat. Recommended sodium intake can be around 300-600mg per hour, adjusted for sweat rate and environmental conditions.
Match your sweat rate: A simple "sweat test" can help you dial in your specific fluid needs by weighing yourself before and after a run.

Choosing Your Fuel: Gels, Chews, or Real Food?

Choosing the right fuel is a personal journey, and what works for one runner may not work for another. It's essential to experiment with different options during training to find what your stomach tolerates best.

Commercial vs. Real Food Fuel


Feature	Energy Gels	Energy Chews	Real Food (e.g., dates, bananas, potatoes)
Carb Delivery	Very quick, rapid absorption for an immediate boost.	Controlled, steady delivery as you can portion intake.	Slower absorption due to fiber content, providing more sustained energy.
Convenience	Easy to carry, single-serving packets, no mess.	Small, portable, and less sticky than gels.	Requires preparation, potentially messy to handle while running.
Digestion	Can cause GI distress if not taken with enough water.	Can be easier on the stomach than gels, especially for lower-intensity runs.	Can be harder to digest during high-intensity efforts due to fat/fiber content.
Satiety	Offers no sense of fullness, can lead to flavor fatigue.	Chewing provides a psychological sense of satiety.	More satisfying and reduces feelings of hunger.
Cost	Can be expensive, especially for long distances.	Generally more expensive than real food alternatives.	Often a cheaper alternative to commercial products.

Training Your Gut for Success

Just as you train your legs and lungs, you can and should train your digestive system to handle fuel during long runs. This process helps minimize GI distress and increases your body's efficiency in absorbing nutrients.

What is Gut Training?

Gut training involves the systematic and consistent practice of consuming fluids and carbohydrates during training sessions to induce physiological adaptations in your gut. Research suggests that a consistent approach can improve gastric emptying and enhance your gut's ability to absorb carbohydrates.

A Step-by-Step Training Plan

Start Early: Begin your gut training 6-10 weeks before your race. It takes time for your gut to adapt, so don't wait until the last minute.
Start Small: Introduce a low carbohydrate intake (e.g., 30g/hr) during your long runs. You can start with liquid calories to get your stomach accustomed to the intake.
Increase Gradually: Progressively increase your carbohydrate intake by 10-15g per hour every few weeks until you reach your target race-day amount (60-90g/hr).
Simulate Race Conditions: Practice your exact race-day nutrition strategy during your key long runs and some faster workouts. This includes your pre-run breakfast and your on-the-run fueling products.
Log Your Intake: Keep a log of your food and fluid intake, as well as any symptoms. This helps you identify what works and what doesn't.

Preventing and Managing GI Distress

Stomach issues can derail a long run, but most are preventable with the right strategy and a bit of practice.

Common Causes of Stomach Issues

Dehydration: Slows down the digestive system, leading to nausea.
Wrong Fuel: High-fiber, high-fat, or high-protein foods can sit heavily in the stomach during exercise.
Over-fueling: Taking in too many carbohydrates or consuming them too quickly can cause cramps and bloating.
Nerves: Pre-race anxiety diverts blood flow away from the gut, exacerbating problems.
New Products: Trying new fuels on race day is a cardinal sin. Stick with what you've practiced.

Practical Tips for a Happy Gut

Time it right: Aim for a simple, carb-heavy snack 1-2 hours before the run.
Fuel early and often: Begin fueling within the first hour and take smaller, more frequent doses (e.g., half a gel every 20-25 minutes) instead of large, infrequent ones.
Dilute gels: Always consume concentrated gels with water to aid digestion.
Listen to your body: If you feel stomach issues, slow down to a walk and sip fluids slowly. Your gut often tolerates fuel better at a lower intensity.

Beyond the Run: The Complete Nutrition Strategy

Proper fueling for a long run is a 24/7 commitment, encompassing your pre-run and post-run nutrition as well.

Pre-Run Fueling

The night before a long run, focus on a balanced, carbohydrate-rich meal. On the morning of, a high-carb, low-fiber, low-fat meal 2-4 hours prior is ideal. Examples include oatmeal, a bagel with jam, or a smoothie. A small, easily digestible snack like a banana can be had closer to the start time.

Post-Run Recovery

The "anabolic window" in the first 30-60 minutes after a hard run is when your muscles are most receptive to nutrients for replenishment. A 3:1 or 4:1 ratio of carbohydrates to protein is considered optimal for restoring muscle glycogen and repairing tissue. Good options include chocolate milk, a protein smoothie with fruit, or Greek yogurt. Continue to eat balanced meals throughout the day to support ongoing recovery.

Conclusion

Mastering how to properly refuel during long runs is a skill that requires as much practice as your running itself. By understanding the fundamentals of carbohydrate and electrolyte intake, experimenting with different fuel types, and methodically training your gut, you can optimize your performance and prevent race-day meltdowns. The key is to start early, practice your strategy consistently, and listen to your body's unique needs. With a little planning and consistency, you can turn your nutrition strategy from an afterthought into a powerful performance-enhancing tool. For further reading on managing nutrition and running, refer to resources like this article on race-day fueling and gut health: Race Training and Gut Health.

Frequently Asked Questions

You should start fueling within the first 30 to 60 minutes of a run that will last longer than 90 minutes. Don't wait until you feel tired or hungry, as by that point, you're already playing catch-up.

Most endurance athletes should aim for 30 to 90 grams of carbohydrates per hour for runs over 90 minutes. For longer events like marathons, 60-90g/hr is a good target, especially when using a dual-source carb mix.

Not necessarily. Energy gels offer rapid absorption and convenience, making them ideal for higher-intensity racing. Real food provides more sustained energy and a greater sense of satiety. The best option depends on your personal preference and race intensity, and should be practiced in training.

Gut training is the practice of consistently consuming fuel and fluids during training runs to teach your digestive system to better tolerate and absorb nutrients during exercise. It's important because it helps prevent GI issues on race day.

For a long run, eat a high-carb, low-fat, and low-fiber meal 2-4 hours beforehand. This could be oatmeal, a bagel, or a smoothie. A smaller snack like a banana can be taken within an hour of starting.

After a long run, consume a snack with a 3:1 or 4:1 carbohydrate-to-protein ratio within 30-60 minutes to replenish glycogen stores and aid muscle repair. Good options include chocolate milk or a fruit smoothie with protein powder.

A sloshing stomach is often caused by drinking too much at once when dehydrated. To prevent this, hydrate consistently with small, regular sips of fluid and electrolytes throughout your run, rather than gulping large amounts when you feel thirsty.

For long runs, especially in hot conditions, electrolytes are necessary. Water alone won't replace the sodium and other minerals lost in sweat, which can lead to dangerously low sodium levels (hyponatremia).