Should You Eat More The Week Before a Marathon? The Truth About Carb Loading

October 21, 2025 •

4 min read

Studies show that effective carbohydrate loading can improve endurance performance by up to 3% in events over two hours. So, should you eat more the week before a marathon? The answer is nuanced, focusing on strategic carbohydrate intake rather than simply increasing overall volume.

Quick Summary

Strategic carb loading in the final 2-3 days before a marathon helps maximize muscle glycogen stores for energy. This involves increasing carbohydrate proportion, not total calories, during your taper.

Key Points

Strategic Carb Loading: Don't just eat more; strategically increase your carbohydrate proportion in the 2-3 days pre-race to maximize energy stores.
Taper and Fuel: During the taper week, reduce training mileage and increase carb intake to help your muscles store energy (glycogen).
Low Fiber is Key: Switch to lower-fiber, easy-to-digest carbs in the final 48 hours to minimize the risk of gastrointestinal issues on race day.
Stay Hydrated: Drink plenty of fluids throughout the week, as water is stored alongside glycogen, aiding both energy reserves and hydration.
Stick to Familiar Foods: Avoid experimenting with new foods or large, heavy meals in the days leading up to the race to prevent stomach upset.
Normal Weight Fluctuation: Expect a temporary weight gain of 2-4 lbs due to increased glycogen and water storage; this is normal and beneficial for race performance.

Understanding the Taper and Glycogen Stores

The final week before a marathon, known as the taper, is a crucial period for both rest and nutrition. During this time, you significantly reduce your training volume, giving your body the chance to repair muscle damage and, most importantly, top off your glycogen stores. Glycogen is the stored form of carbohydrates in your muscles and liver, and it is the primary fuel source your body uses during high-intensity, long-duration exercise, like a marathon. The goal of eating the week before a marathon isn't necessarily to eat 'more' food, but rather to shift the composition of your diet to prioritize carbohydrates over fats and proteins.

Your body can only hold a finite amount of glycogen, typically enough to fuel around 90 minutes of intense activity. By following a proper carb-loading protocol in the 2-3 days leading up to the race, you can maximize these stores, helping to delay fatigue and avoid "hitting the wall". This strategy allows you to begin the race with a full tank of energy, giving you the best chance to perform at your peak.

The Carb-Loading Timeline

While the entire week is part of your race week nutrition plan, the heavy lifting of carb loading happens in the final 36-48 hours. Here is a typical breakdown:

Days 7-4 Pre-Race: During the initial part of your taper, continue with a balanced diet that is high in carbohydrates but includes moderate amounts of protein and healthy fats. This allows your body to continue recovering and to slowly build up glycogen stores as your mileage decreases. Focus on complex carbohydrates during this time, which provide sustained energy and are nutrient-dense.
Days 3-1 Pre-Race: This is the prime carb-loading phase. Your diet should now be 85-95% carbohydrates. To avoid gastrointestinal (GI) distress during the race, it's wise to start focusing on lower-fiber carbohydrates. This shift is about prioritizing carbs, so you will naturally eat less protein and fat. Spreading your meals throughout the day (5-6 smaller meals) rather than eating three huge ones can also help prevent a heavy, bloated feeling. Don't be alarmed by a small amount of weight gain during this time, as it's just water retained with the stored glycogen.
The Night Before: Your pre-race dinner should be a familiar, carbohydrate-heavy meal with moderate protein and low fiber. Eat on the early side to give your body ample time to digest. A simple pasta with marinara sauce or a baked potato are classic examples. Avoid trying any new or spicy foods that could cause stomach issues.

Best Practices for Successful Race Week Nutrition

List of Recommended Foods for Carb Loading

Grains: White pasta, white rice, bagels, pretzels, low-fiber cereal (e.g., cornflakes)
Fruits: Bananas, peeled apples or applesauce, fruit juice
Vegetables: Peeled potatoes, sweet potatoes, and other starchy vegetables
Dairy (if tolerated): Low-fat yogurt, milk
Supplements: Sports drinks, energy gels, and energy bars can help meet carb targets without feeling overly full

Marathon Week Eating: Strategic Intake vs. "More Is Better"


Aspect	'More is Better' Myth	Strategic Carb Loading Reality
Calorie Intake	Increases total food intake drastically, often with high-fat, high-protein foods.	Prioritizes carbohydrates, often keeping overall calories similar to high-volume weeks during the taper.
Nutrient Ratio	Imbalanced, leading to excessive intake of fat, protein, and fiber.	Carefully manages macronutrient ratios to favor carbohydrates for energy storage.
Gastrointestinal Effects	High risk of bloating, indigestion, and mid-race GI distress from excess fiber and fat.	Minimizes risk of stomach issues by reducing fiber in the final 2-3 days.
Food Choices	Includes unfamiliar foods or high-fat "reward" meals.	Focuses on familiar, easy-to-digest carbohydrate sources.
Goal	Simply to eat a lot.	To maximize muscle glycogen stores and optimize race performance.

The Role of Hydration and Electrolytes

Proper hydration is just as important as carbohydrate intake during race week. Glycogen is stored with water, so increasing your fluid intake is essential for effective carb loading and for preventing dehydration during the race. Make sure to drink plenty of water and consider incorporating electrolyte-rich beverages, especially in the final 48 hours. This ensures your body is primed and ready for the demands of the marathon.

Conclusion

In conclusion, the approach to eating the week before a marathon is not about mindlessly eating more food. It is a calculated and strategic process known as carb loading. By gradually increasing the proportion of carbohydrates in your diet while reducing training volume, you maximize your body's energy reserves. Focusing on low-fiber, familiar foods in the final days and prioritizing hydration are key to ensuring you arrive at the start line with full glycogen stores and a settled stomach. Trust the taper and your nutrition plan to deliver your best race performance.

For more detailed guidance, consider consulting resources like Runner's World for expert advice on marathon nutrition.

Frequently Asked Questions

You should begin the strategic increase of carbohydrates in your diet approximately 36-48 hours before the marathon, not a full week in advance.

The main purpose is to maximize your muscle glycogen stores. Glycogen is the most accessible energy source for your body during endurance events and helps prevent early fatigue.

Yes, it is normal to gain 2-4 pounds during the carb-loading period. This is mostly water weight, as glycogen stores require water to be stored in the muscles.

You should avoid trying new or unfamiliar foods, high-fat meals, and excessive fiber, especially in the final 48 hours, to prevent digestive issues.

It is generally more effective and comfortable to consume 5-6 smaller meals or snacks throughout the day, rather than large, heavy meals. This helps avoid bloating and lethargy.

Hydration is crucial. In addition to water, consuming electrolyte beverages can help your body store glycogen and prepare for fluid loss during the race.

Your last meal, eaten 2-3 hours before the race, should be a high-carbohydrate, low-fiber, and moderate-protein meal that you have practiced with during training. Examples include a bagel with peanut butter or oatmeal.