Planning Your Nutrition for a Marathon or Half Marathon

Running a marathon or half-marathon isn't just about physical training. Many passionate runners, even experienced ones, have already experienced it: despite rigorous preparation, the race can turn into an ordeal if nutrition hasn't been thought through in advance. Stomach aches, a "slump" at the 30th kilometer, cramps, or even dropping out... all these problems often stem from an ill-adapted nutritional strategy.

Nutrition is often described as the third discipline of endurance, after training and recovery. Preparing your meal plan is therefore essential to optimize your performance, but also to fully enjoy the experience.

This article offers you a clear and progressive nutritional strategy, designed for autumn marathons (Valencia, Florence, etc.) but also for those of spring 2026 (Paris, Rotterdam, etc.). You will find practical advice, accessible scientific explanations and even a simplified calculator with concrete examples for 2h, 3h or 4h objectives.

Copyright: Namur Marathon

1. Understanding the energy needs of the marathon runner

Before planning what to eat, it is essential to understand the physiological constraints 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 short, but still demanding: its duration varies from 1 to 3 hours.

Energy expenditure

On average, a runner burns between 800 and 1100 kcal per hour depending on their weight, pace and running efficiency. Over a marathon, this represents a total expenditure of 2000 to 4000 kcal, sometimes more.

The body has two main sources of energy:

• glycogen, stored in the muscles and the liver, which constitutes the main fuel for intense efforts,

• lipids, very abundant but mobilized more slowly.

A well-trained athlete can store approximately 400 to 600 g of glycogen, or between 1600 and 2400 kcalThese reserves are sufficient for a half marathon, but they do not cover all the needs of a marathon, especially if you run fast.

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

2. The pre-race nutritional strategy

Good nutrition doesn't stop at the big day. It starts several days before the competition, with a clear goal: 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 two or three days before the race to saturate the muscles with glycogen. We are talking about glycogen overcompensation.

Concretely, 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 daily carbohydrates.

Examples of foods to favor:

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

• compotes, ripe bananas, rice cakes,

• fruit juice, honey, jam.

Conversely, avoid foods that are too rich in fiber (raw vegetables, dried vegetables), heavy fats (dishes in sauce, fried foods) and alcohol.

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

b) The last meal: 3 to 4 hours before departure

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

Example for a 9am marathon:

• 2 slices of white bread with jam,

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

• 1 very ripe banana,

• a coffee or tea if the body is used to it.

Example for a half marathon at 13 p.m.:

• a light brunch around 9–10 a.m.: oatmeal porridge, compote, bread with honey, hot drink.

c) The pre-race snack

Between 15 and 30 minutes before departure, a small top-up is useful. This can take the form of a energy gel or a few sips of a carbohydrate drink. This helps stabilize blood sugar levels when you leave.

3. Nutrition during the race

This is the trickiest step. Many runners fail not because they lack training, but because they fail to fuel properly during races.

a) The objectives

• Maintain a regular carbohydrate intake to preserve muscle glycogen.

• Stabilize blood sugar to avoid reactive hypoglycemia.

• Provide electrolytes to compensate for sweat losses.

• Avoid digestive disorders.

Current recommendations state:

• 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 for absorption.

b) Sources of carbohydrates

• Energy gels : easy to transport, provide 20–30 g of carbohydrates each.

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

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

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

c) Hydration

It is not enough to swallow gels: they must be accompanied by water. A simple rule is to drink 400 to 800 ml per hour, depending on temperature, humidity and individual perspiration.

Water alone is not enough: you also need to compensate for sodium losses, the main cause of cramps. We recommend 500 to 800 mg of sodium per liter of drink.

https://www.ta-energy.com/

d) Training the digestive system

Like muscles, the gut needs training. Testing your gels, drinks, and carbohydrate intake during a long run is essential to avoid unpleasant surprises on the day.

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

Now let's move on to practice with three concrete scenarios.

 

Concrete example for a 3-hour marathon:

• Departure: 1 gel just before.

• Km 7, 14, 21, 28: 1 gel each time.

• Between refuelings: regular sips of carbohydrate drink.

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

5. Recovery after the race

Once the line is crossed, the mission is not over. Recovery begins in the first 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 within one hour of the race.

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

• liquids : 1,5 times the weight lost (example: if loss of 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 bananas,

• 1 drinking yogurt,

• 500 ml of mineralized water.

6. Common mistakes to avoid

1. Testing a gel on race day → always try in training.

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

3. Overindulging in coffee or stimulants → digestive or cardiac risk.

4. Neglecting sodium → Cramps often come from an electrolyte imbalance.

5. Deprive yourself of carbohydrates the week before → a “low carb” strategy can sabotage performance.

Conclusion

Marathon and half-marathon nutrition isn't a minor detail: it's a strategy in its own right, as important as training sessions or choosing the right shoes. When well-planned and tested in advance, it allows you to push back the infamous "marathon wall," avoid fatigue, and fully enjoy your race.

Remember:

• Before the race, fill your reserves.

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

• after the race, recover actively with carbohydrates + proteins.

By integrating these principles and adapting the strategy to your profile, you put all the chances on your side to succeed in your next 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 adapted to your needs, whether you are aiming for 2 hours, 3 hours or 4 hours.

Fast Mini Calculator

• Half marathon: aim for 30–60g carbs/hr.

• Marathon: Aim for 60–90g carbs/hr.

• Simplified formula :
  Glucides/h = (Poids en kg x 1 à 1,2 g) selon intensité et tolérance.