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 diet. However, an optimized marathon diet is not limited to the meal consumed the day before. Carbohydrates, proteins, fats, 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, especially 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 mainly converted into glucose. This glucose can be used immediately as fuel or stored as glycogen. During a moderate to high-intensity race like a marathon, these reserves are mobilized to sustain the effort and maintain stable blood sugar levels.

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

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 feeling of general exhaustion.

Gastrointestinal issues such as nausea, stomach pain, flatulence, bloating, diarrhea, or reflux are common in endurance sports. They can be aggravated by an excess of fiber, inadequate hydration, poor tolerance to certain gels, or too 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 diet: 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 starchy foods (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 compote or a simple sweet product;
• water as the main beverage.

From the 4th day before the race, gradually start reducing foods very high in fiber such as legumes, whole grains, or certain raw vegetables.

D-3 to D-1: carbohydrate loading

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

In practice, if you're running on Saturday, you should start from Wednesday to increase your carbohydrate intake until it reaches 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 an effective increase in glycogen stores, without resorting to old methods such as the modified dissociative diet (Bussau et al., 2002).

Preferred sources:

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

 

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).

Example meal:

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

It is best 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 the morning of the marathon?

Breakfast before the race

The pre-marathon breakfast is usually the last meal before 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 a 70 kg athlete).
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 of marathon runners, it was observed that runners who consumed 60 to 90 g/h of carbohydrates during the competition were more likely to finish in under 180 minutes (3 h).

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

Practical sources:

• fruits (banana);
• white bread with honey;
• compotes 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 approximately 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 hours after finishing, 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.

Example post-race snack

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 fruits and honey.

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

 

Common marathon nutrition mistakes

Believing 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 during training can cause digestive issues during the race.

Calorie restriction

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

Overhydrating before the start

Drinking excessively just before running does not improve performance and can lead to 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.

Certain products can nevertheless prove useful: energy gels, sports drinks, electrolyte tablets.

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

 

Example of a typical 7-day pre-marathon menu

Race Day

Toast + honey + very ripe banana + water

—

(during) gels/energy drinks/fruit purees

(after) recovery drink + full meal

Marathon Nutrition FAQ

What to eat 3 days before a marathon?

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

How many carbohydrates do you need before a marathon?

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

Can you drink coffee before a marathon?

Yes, if you are used to it. Caffeine (3 to 6 mg/kg) can improve endurance performance. Test it in 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 load over 1 to 3 days.

What to 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 isotonic drinks.

In summary: Key takeaways

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

Remember these principles:

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

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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