Marathon Nutrition: The Complete Guide to Performing on Race Day

Why do so many well-trained marathon runners collapse after the 30th kilometer? Sometimes, it's because physical preparation alone is not enough.

Over 42.195 km, your performance depends as much on your legs as on your plate. Optimized marathon nutrition, however, is not limited to the meal the night before. Carbohydrates, proteins, lipids, timing, and quantity: discover how to plan your nutritional strategy to cross the finish line in the best possible conditions.

 

Why is nutrition crucial for a marathon?

Running 42.195 km intensely mobilizes your energy reserves, particularly muscle and liver glycogen (stored in the liver). However, these stores are limited and cannot always cover the energy expenditure induced by a marathon (BI Report, 2010). Hence the need to develop a specific dietary strategy to prevent their depletion.

The role of carbohydrates and glycogen

The carbohydrates you consume serve as fuel for your muscles. Once digested, they are primarily converted into glucose. This glucose can be used immediately as fuel or stored as glycogen. During a moderate to high-intensity run like a marathon, these reserves are mobilized to sustain effort and maintain stable blood sugar levels.

According to the International Society of Sports Nutrition (ISSN) position, the ability to sustain effort in endurance sports largely depends on your carbohydrate reserves. When these diminish, your performance gradually decreases.

The risks of a poor nutritional strategy

A poorly adapted marathon nutrition plan can lead to premature depletion of carbohydrate reserves. Also known as "hitting the wall," it manifests as a sudden drop in performance, intense fatigue, heavy legs, difficulty concentrating, and a general feeling of exhaustion.

Gastrointestinal issues such as nausea, stomach pain, flatulence, bloating, diarrhea, or reflux are common in endurance sports. They can be exacerbated by excessive fiber intake, inadequate hydration, poor tolerance to certain gels, or late or excessive carbohydrate intake (De Oliveira et al., 2014).

You may also face dehydration or hyponatremia (excessive dilution of blood sodium due to excessive water consumption).

 

Marathon nutrition: what to eat the week before?

D-7 to D-4: balanced diet

During the first part of the pre-marathon week, eat a balanced and varied diet, prioritizing at each meal:

• a source of starches (rice, pasta, potatoes, bread, quinoa, etc.);
• a source of protein (fish, meat, eggs, dairy products, legumes, etc.);
• quality fats (olive oil, avocado, nuts, etc.);
• raw or cooked vegetables depending on your digestive tolerance;
• a fruit or applesauce or a simple sugary product;
• water as the main beverage.

Starting from the 4th day before the race, gradually reduce foods very rich in fiber such as legumes, whole grains, or certain raw vegetables.

D-3 to D-1: carbohydrate loading (carb loading)

The 36 to 48 hours before the competition are a key period.

In practice, if you are running on Saturday, you should start from Wednesday to increase your carbohydrate intake until you reach 10 to 12 g per kilogram of body weight depending on your training level and digestive tolerance.

This overload, combined with a reduction in your training volume, generally allows for effectively increasing glycogen stores, without resorting to old methods like the modified dissociated diet (Bussau et al., 2002).

Preferred sources:

• brioche, simple biscuits;
• honey, syrup, jam, fruit juice;
• potatoes (mashed, steamed, baked);
• white bread, white pasta, semolina, white rice;
• ripe banana, apple sauce, pear sauce, apricot sauce…

 

What to eat the day before a marathon?

The dinner the night before should be rich in carbohydrates, moderate in protein, low in fat and fiber. Consume it relatively early to limit the risk of digestive discomfort the next morning (Thomas et al., 2016).

Meal example:

• rice or white pasta;
• a drizzle of olive oil;
• small portion of cooked vegetables;
• plain yogurt + fruit or compote;
• omelet, grilled chicken or lean fish.

It is preferable to completely limit:

• alcohol;
• very fatty dishes;
• very spicy dishes;
• large quantities of raw vegetables for sensitive individuals;
• unusual foods never tested before the competition.

What to eat on marathon morning?

Breakfast before the race

Breakfast before a marathon is generally the last meal for a morning race. Otherwise, current recommendations suggest consuming the last meal 1 to 4 hours before running.

Consume 1 to 4 g of carbohydrates per kg (i.e., 70 to 280 g for an athlete weighing 70 kg).
Drink approximately 5 to 7 mL/kg in the 2 to 4 hours before the effort.

 

Nutrition during the marathon

Carbohydrate intake during the race

In a descriptive study on marathon runners, it was observed that runners who maintained carbohydrate intakes of 60 to 90 g/h during the competition were more likely to finish in under 180 minutes (3 hours).

You can go up to 120 g/h only if the strategy has been tested, digestive training ("gut training") has been performed, and the intake combines glucose + fructose.

Practical sources:

• fruits (banana);
• white bread with honey;
• fruit purees in pouches;
• energy bars;
• homemade or commercial energy gels;
• isotonic drink with a concentration of 5 to 8%.

Hydration management

The American College of Sports Medicine (ACSM) recommends an average of 400 to 800 mL of fluid per hour, or about 150 to 200 mL every 15 to 20 minutes.

In case of heat or heavy sweating, plan for water or a drink containing electrolytes, especially sodium.

To learn more about how to manage your hydration during a marathon, read our dedicated guide.

 

Post-marathon nutrition: optimizing recovery

Metabolic window

In the first few hours after the finish, an effective strategy is to consume: 1 to 1.2 g of carbohydrates/kg according to the ACSM. You can combine 20 to 30 g of protein. This combination accelerates glycogen resynthesis and initiates muscle recovery.

Post-race snack example

Here are some simple, realistic, and easy-to-digest options:

• recovery drink: whey + milk or water + banana;
• homemade smoothie (banana + plain yogurt + honey + milk);
• Greek yogurt or cottage cheese with fruit and honey.

Then follow up within 4 hours with a full meal such as: chicken or fish + white rice or sweet potato.

 

Common marathon nutrition mistakes

Believing that a plate of pasta is enough

Carbohydrate loading is built over 24 to 48 hours, not just one meal.

Using new products on race day

Gels, energy drinks, bars, or supplements never tested in training can cause digestive problems during the race.

Calorie restriction

Losing weight the week before the event reduces energy reserves and can compromise performance and recovery.

Over-hydrating before the start

Drinking excessively just before running does not improve performance and can promote digestive discomfort or hyponatremia.

Neglecting sodium in hot conditions

In summer or with heavy sweating, insufficient sodium intake can lead to decreased performance, cramps, or, more rarely, hyponatremia.

 

Should I take food supplements?

According to Wirnitzer et al. (2021), about 50% of endurance runners report consuming food supplements, mainly vitamins. However, in the absence of a proven deficiency, the benefits of such supplementation are limited.

Some products can nevertheless be useful: energy gels, sports drinks, electrolyte tablets.

Whatever the case, before considering any supplementation (iron, vitamin D, zinc, magnesium), it is best to seek advice from a dietitian specializing in sports nutrition.

 

Example of a typical 7-day pre-marathon menu

FAQ – Marathon Nutrition

What to eat 3 days before a marathon?

Prioritize digestible carbohydrates: white bread, rice, pasta, potatoes, ripe bananas, and compotes. Maintain moderate protein intake (lean meat, fish, eggs).

How many carbohydrates should I have before a marathon?

It is recommended to consume 10 to 12 g per kilogram of body weight during the 36 to 48 hours preceding the race.

Can you drink coffee before a marathon?

Yes, if you're used to it. Caffeine (3 to 6 mg/kg) can improve endurance performance. Test it during training.

Should you have a pasta party?

A pasta party can help, but it's not enough on its own. It should be part of a carbohydrate loading strategy over 1 to 3 days.

What should you eat to avoid "hitting the wall" during a marathon?

Saturate your reserves with carbohydrate-rich foods during the 36 to 48 hours before the race. During the marathon, regularly consume gels, bars, or an isotonic drink.

In summary: What to remember

A marathon is an endurance event that mobilizes your energy reserves to their limits. That's why you need to focus on a well-designed marathon nutrition strategy.

Remember these principles:

• carbohydrate loading 36 to 48 hours before the race;
• a digestible dinner the night before;
• a suitable breakfast;
• regular refueling from the first kilometers;
• controlled hydration;
• immediate recovery with carbohydrates + proteins.

Runners who follow these recommendations increase their chances of achieving their goal.

Good nutritional preparation does not replace training, but it can clearly make the difference between suffering through the race and finishing it in good condition.

 

Bibliography

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