Plan your nutrition for a marathon or half-marathon

Running a marathon or half marathon is not just a matter of physical training. Many passionate runners, even experienced ones, have already experienced this: despite thorough preparation, the race can become a nightmare if nutrition has not been planned in advance. Stomach aches, hitting the wall at the 30th kilometer, cramps, or even dropping out—all these problems often stem from an unsuitable nutrition strategy.

Nutrition is often described as the third discipline of endurance sports, after training and recovery. Preparing your nutrition plan is therefore essential not only to optimize your performance but also to fully enjoy the experience.

This article offers a clear, progressive nutrition strategy designed for autumn marathons (Valencia, Florence, etc.) as well as spring 2026 races (Paris, Rotterdam, etc.). You will find practical advice, accessible scientific explanations, and even a simplified calculator with concrete examples for 2-, 3-, or 4-hour goals.

Copyright: Namur Marathon

1. Understanding the marathon runner's energy needs

Before planning what to eat, it is essential to understand the physiological demands of a marathon or half marathon.

A marathon represents 42.195 km of continuous effort, lasting between 2 and 6 hours depending on the runner's level. The half marathon (21.1 km) is half as long, but it remains demanding: its duration varies from 1 to 3 hours.

Energy expenditure

On average, a runner burns between 800 and 1,100 kcal per hour depending on their weight, pace, and running efficiency. Over a marathon, this represents a total expenditure of 2,000 to 4,000 kcal, sometimes more.

The body has two main sources of energy:

• glycogen, stored in the muscles and liver, which serves as the primary fuel for intense efforts,

• fat, which is abundant but mobilized more slowly.

A well-trained athlete can store approximately 400 to 600 g of glycogen, equivalent to between 1,600 and 2,400 kcal. These reserves are sufficient for a half marathon, but they do not cover all the needs of a marathon, especially when running fast.

This is why, after the 30th kilometer, many runners encounter the famous “marathon wall”: glycogen runs out, fatigue becomes overwhelming, and the legs feel heavy. The only way to push back this wall is to consume carbohydrates regularly during the race.

2. The pre-race nutrition strategy

Good nutrition is not limited to race day. It begins several days before the competition, with a clear objective: arrive at the start with optimal glycogen stores and a ready digestive system.

a) The week before the race: the role of “carbo-loading”

The principle is simple: increase carbohydrate intake in the two or three days before the race to saturate the muscles with glycogen. This is known as glycogen supercompensation.

In practical terms, this means consuming 8 to 10 g of carbohydrates per kilogram of body weight per day on D-2 and D-1. For a 65 kg runner, this represents 520 to 650 g of carbohydrates per day.

Examples of foods to prioritize:

• white rice, pasta, semolina, white bread, potatoes,

• applesauce, ripe bananas, rice cakes,

• fruit juice, honey, jam.

Conversely, avoid foods that are too high in fiber (raw vegetables, legumes), heavy fats (sauced dishes, fried foods), and alcohol.

Source: https://www.meltonic.com/fr/blog

b) The last meal: 3 to 4 hours before the start

This meal should be rich in easily digestible carbohydrates, moderate in protein, and very low in fat and fiber.

Example for a marathon at 9 a.m.:

• 2 slices of white bread with jam,

• 1 serving of rice or semolina with a drizzle of honey,

• 1 ripe banana,

• coffee or tea if your body is accustomed to it.

Example for a half marathon at 1 p.m.:

• a light brunch around 9–10 a.m.: oat porridge, applesauce, bread with honey, and a hot drink.

c) The pre-race snack

Between 15 and 30 minutes before the start, a small energy boost is useful. This could be an energy gel or a few sips of a carbohydrate drink. This helps stabilize blood sugar at the start.

3. Nutrition during the race

This is the most delicate stage. Many runners fail not because they lack training, but because they are unable to fuel themselves properly during the race.

a) The objectives

• Maintain a regular carbohydrate intake to preserve muscle glycogen.

• Stabilize blood sugar to prevent reactive hypoglycemia.

• Provide electrolytes to compensate for losses through sweat.

• Avoid digestive issues.

Current recommendations indicate:

• Half marathon: 30 to 60 g of carbohydrates per hour.

• Marathon: 60 to 90 g of carbohydrates per hour, or even up to 100–120 g/h for elites trained in absorption.

b) Sources of carbohydrates

• Energy gels: easy to carry and provide 20–30 g of carbohydrates each.

• Isotonic drinks: 30–40 g of carbohydrates per 500 ml.

• Sports bars and fruit purées: useful for varying textures, but pay attention to digestibility.

The ideal combination contains glucose and fructose in a 2:1 ratio to maximize intestinal absorption.

c) Hydration

It is not enough to consume gels: they must be taken with water. A simple rule is to drink 400 to 800 ml per hour, depending on the temperature, humidity, and individual sweating.

Water alone is not enough: you also need to replace sodium losses, which are primarily responsible for cramps. We recommend 500 to 800 mg of sodium per liter of drink.

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d) Digestive system training

Like muscles, the gut can be trained. Testing your gels, drinks, and carbohydrate quantities during long runs is essential to avoid unpleasant surprises on race day.

4. Practical examples: strategies for 2h / 3h / 4h

Let’s now move on to practice with three concrete scenarios.

 

Concrete example for a 3-hour marathon:

• Start: 1 gel just before.

• Km 7, 14, 21, 28: 1 gel each time.

• Between aid stations: regular sips of a carbohydrate drink.

This strategy provides approximately 240 g of carbohydrates over 3 hours, or 80 g/h, which is ideal for this profile.

5. Recovery after the race

Once you cross the finish line, the mission is not over. Recovery begins within the first few minutes.

a) The metabolic window

In the 30 to 60 minutes following exercise, the body is particularly receptive to nutritional intake. This is the ideal time to restore glycogen stores and initiate muscle repair.

b) Recommendations

• Carbohydrates: 1–1.2 g/kg in the hour following the race.

• Protein: 20–30 g to promote muscle recovery.

• Fluids: 1.5 times the weight lost (example: if you lose 2 kg, drink 3 liters in the following hours).

• Sodium: essential for retaining water and rehydrating effectively.

c) Example of a post-marathon snack

• 1 recovery drink (30 g protein + 50 g carbohydrates),

• 1 banana,

• 1 drinking yogurt,

• 500 ml of mineral water.

6. Common mistakes to avoid

1. Trying a gel on race day → always test it in training.

2. Starting too fast without fueling → waiting until the 20th km is a classic mistake.

3. Overdoing coffee or stimulants → digestive or cardiac risk.

4. Neglecting sodium → cramps often result from an electrolyte imbalance.

5. Avoiding carbohydrates the previous week → a “low-carb” strategy can sabotage performance.

Conclusion

Nutrition for the marathon and half marathon is not a detail: it is a strategy in its own right, just as important as your training sessions or choice of shoes. When well planned and tested in advance, it helps you push back the famous “marathon wall,” avoid energy crashes, and fully enjoy your race.

Remember:

• Before the race, replenish your stores.

• During the race, consume carbohydrates regularly and hydrate with electrolytes.

• After the race, actively recover with carbohydrates + protein.

By incorporating these principles and adapting the strategy to your profile, you give yourself every chance of succeeding in your upcoming autumn marathons (Valencia, Florence) or your major 2026 events (Paris, Rotterdam).

And to put these tips into practice, explore the Nutribay catalog: you will find gels, drinks, bars, and supplements perfectly suited to your needs, whether you are aiming for 2, 3, or 4 hours.

Quick calculator

• Half marathon: aim for 30–60 g of carbohydrates/h.

• Marathon: aim for 60–90 g of carbohydrates/h.

• Simplified formula:
  Carbohydrates/h = (Weight in kg x 1 to 1.2 g) depending on intensity and tolerance.