How to Fuel During a Marathon: Your Guide to Optimal Race Day Nutrition

October 2, 2025 •

5 min read

Approximately 31% of amateur runners arrive at a race already dehydrated. Mastering how to fuel during a marathon is a critical component of race preparation that, alongside training, ensures you have the energy to cross the finish line feeling strong. A well-rehearsed nutrition strategy is your best defense against 'hitting the wall'.

Quick Summary

This article outlines essential fueling strategies for marathon day, including pre-race preparation, mid-race intake of carbohydrates and electrolytes, and post-race recovery nutrition. It emphasizes practicing your plan during training to ensure race-day success and avoid gastrointestinal issues.

Key Points

Train Your Gut: Practice your race day fueling strategy during long training runs to acclimate your stomach to the products and timings.
Carb-Load Correctly: Two to three days before the race, increase your carbohydrate intake while reducing fat and fiber to maximize glycogen stores.
Start Fueling Early: Begin taking in carbohydrates 30-45 minutes into the race to stay ahead of glycogen depletion and avoid hitting the wall.
Don't Overlook Hydration and Electrolytes: Match your fluid intake to your sweat rate and replenish lost electrolytes to prevent dehydration and hyponatremia.
Stick to What You Know: Avoid experimenting with new gels, foods, or gear on race day to prevent unexpected GI issues.
Prioritize Post-Race Recovery: Consume a carbohydrate and protein snack within an hour of finishing to begin the recovery process.

The Science of Marathon Fueling

To understand how to fuel during a marathon, you must first understand the body's energy systems. During prolonged, high-intensity exercise like a marathon, your body primarily relies on carbohydrates for energy. These carbohydrates are stored in your muscles and liver as glycogen. A typical runner can only store enough glycogen to last about 90 to 120 minutes of running at marathon pace. Once these stores are depleted, performance declines rapidly—a phenomenon known as 'hitting the wall' or 'bonking'.

Effective fueling during a marathon, therefore, is not about finding a magical energy source mid-race; it is about consistently topping off your glycogen stores and maintaining blood sugar levels to prevent that dreaded crash. This process is highly individual and requires careful planning and practice during your training period.

Strategic Carb-Loading: The Days Before

Carbohydrate loading is a crucial component of pre-race preparation, but it is not a free pass to binge on pasta the night before. Instead, it involves increasing your carbohydrate intake and reducing fat and fiber for two to three days before the race. This strategy super-saturates your muscles with glycogen, providing a larger starting fuel tank for race day.

Increase Carbohydrate Percentage: Aim for 70-80% of your total calories to come from carbohydrates, while slightly reducing protein and fat intake.
Eat Familiar Foods: Stick to foods you regularly eat and know your stomach tolerates well to avoid last-minute gastrointestinal (GI) issues.
Prioritize Low Fiber: In the final 24-48 hours, opt for lower-fiber carbs like white pasta, rice, and bagels over whole-grain varieties to minimize the risk of a mid-race bathroom emergency.

The Race Morning Meal

On race morning, your goal is to top up your liver glycogen stores, which have been used overnight. This meal should be familiar, high in easily digestible carbohydrates, and low in fat and fiber.

Timing is Everything: Eat your pre-race meal 2-4 hours before the start to allow for proper digestion.
Fueling Options: Great choices include oatmeal with a banana and honey, a bagel with jam, or toast with peanut butter.
Pre-Race Top-Up: For an extra boost, consider a quick-digesting carb snack, like an energy gel or chews, 15-20 minutes before the starting gun.

Fueling During the Marathon

During the race, your body's ability to absorb carbohydrates is limited, but consistent intake is vital. The general recommendation is to consume 30-60 grams of carbohydrates per hour for most runners, with some elite athletes pushing for 60-90 grams per hour.

Mid-Race Fueling Strategies

Start Early: Begin consuming fuel 30-45 minutes into the race, before you feel depleted. Don't wait for your energy to dip.
Consistency is Key: Take in small, regular amounts of fuel every 20-30 minutes, rather than large doses infrequently, to maintain a steady energy supply.
Listen to Your Body: If you experience stomach discomfort, slow down your intake or temporarily stop until you feel better. You can't force your stomach to absorb fuel faster than it's able.

Comparing Mid-Race Fuel Options


Fuel Source	Carbohydrate Content	Pros	Cons
Energy Gels	20-40g+ per sachet	Lightweight, portable, easy to absorb, fast-acting energy. Many options including caffeine.	Can be messy, sticky, and some find the taste and texture hard to stomach over time.
Energy Chews	~20-30g per serving	Solid feel offers a psychological boost, easy to regulate intake by consuming one chew at a time.	Chewing can be difficult during high-intensity running; some may find them too sugary.
Sports Drinks	~30-60g per 500ml	Combines hydration and carbs, good for those with sensitive stomachs who dislike gels.	Can be bulky to carry, risks over-consuming fluids or carbs if not managed carefully.
Real Food	Variable (e.g., banana ~25g)	A natural, palatable alternative. Can settle stomach and provide satiety.	Harder to digest and carry, more challenging to eat on the move.

Hydration and Electrolytes: The Other Side of the Coin

Proper hydration is just as important as fueling. Dehydration can impair performance and increase the risk of heat-related illnesses. Replacing lost electrolytes, especially sodium, is also critical for maintaining fluid balance and muscle function.

Pre-load with Electrolytes: Drink a sodium-rich electrolyte drink the evening and morning before the race to maximize fluid retention.
Monitor Your Sweat Rate: Practice measuring your fluid loss during training to dial in your personal hydration needs. Most runners need between 300-800ml of fluid per hour, depending on conditions and pace.
Don't Overdrink: Excessive fluid intake without adequate electrolytes can lead to a dangerous condition called hyponatremia. Don't drink so much that you gain weight during the race.
Combine for Efficiency: Many sports drinks and gels contain both carbohydrates and electrolytes, which can be an efficient way to manage both needs.

The Role of Caffeine

Caffeine can be a legal and effective ergogenic aid for endurance events, shown to enhance performance by reducing the perception of effort. However, it affects everyone differently and should be practiced in training first.

Pre-Race Dose: Some athletes benefit from a dose of caffeine (3-6 mg per kg of body weight) 30-60 minutes before the start.
Mid-Race Boost: A smaller dose in the later stages of the race can provide a welcome lift when fatigue sets in.
Start with Small Doses: If new to caffeine, start with a low dose (20-30mg) to assess your tolerance.

Post-Race Recovery

Once you cross the finish line, your fueling journey isn't over. The 30-60 minute window immediately post-race is the prime time to kickstart muscle repair and glycogen replenishment.

The 3:1 Ratio: Aim for a snack with a 3:1 ratio of carbohydrates to protein. Chocolate milk is a classic for a reason.
Replenish and Rehydrate: Continue drinking fluids with electrolytes. Weigh yourself post-race to estimate fluid loss and aim to replace 1.5 times the weight lost.
Subsequent Meals: Focus on balanced meals rich in carbs, lean protein, and healthy fats in the hours and days following the marathon to continue the recovery process.

Conclusion

Fueling successfully for a marathon goes far beyond what you do on race day. It is an ongoing process of preparation, practice, and personalization. By training your gut to handle your chosen fuel, understanding your unique hydration needs, and sticking to a well-tested plan, you can avoid hitting the wall and maximize your performance. The key is to experiment with different foods and products during your long training runs. This rehearsal ensures there are no surprises on race day, giving you the confidence and energy to perform at your best. While sports nutrition products are convenient, remember to incorporate whole foods into your training diet for a wider array of nutrients.

MOTTIV offers a comprehensive guide to marathon training nutrition, including race day advice.

Frequently Asked Questions

Hitting the wall, or 'bonking,' occurs when your body's glycogen stores are depleted. You'll experience severe fatigue, your pace will drop significantly, and every step will feel like a massive effort. It is largely preventable with a smart fueling strategy.

A general guideline is 30-60 grams of carbohydrates per hour for most runners, although more experienced athletes may train their gut to handle up to 90 grams per hour. The amount depends on your pace, size, and what your body can tolerate.

For runs over 90 minutes, electrolytes are crucial. You lose essential minerals like sodium and potassium through sweat, and only drinking water can dilute your blood sodium, potentially causing hyponatremia. Electrolytes help maintain fluid balance and muscle function.

The best breakfast is one you've tested in training. Opt for easily digestible carbohydrates like oatmeal, a bagel with jam, or a banana, eaten 2-4 hours before the race. Avoid high-fat, high-fiber, and high-protein foods that can upset your stomach.

Caffeine can boost endurance and focus, but you must test your tolerance during training. Many runners take a dose before the race and another smaller dose later to counter fatigue. Start with a low dose and see how your body reacts.

There are several options for carrying fuel, including running belts with gel loops, hydration vests, or specialized apparel with pockets. For hydration, you can carry a handheld bottle or a hydration pack, or rely on aid stations.

Yes, some runners prefer real food like bananas, dried fruit, or even gummy bears. However, real food can be harder to digest on the move and might not provide the same amount of fast-acting carbs as a gel. Test what works for your stomach during training.