What nutrients does a marathon runner need?

November 21, 2025 •

4 min read

According to the International Society of Sports Nutrition, endurance athletes like marathon runners can require up to 7,000 calories per day during peak training to fuel their bodies adequately. Knowing what nutrients does a marathon runner need is critical for preventing fatigue, supporting muscle repair, and maximizing performance over 26.2 miles.

Quick Summary

Running a marathon requires a precise nutritional strategy focusing on key macronutrients and micronutrients. The focus is on complex carbohydrates for sustained energy, timed protein for muscle recovery, and crucial electrolytes for hydration and performance, with specific attention to iron and vitamin D. Strategic fueling before, during, and after training supports optimal performance and recovery.

Key Points

Carbohydrates are the primary fuel: The body's main energy source for a marathon is carbohydrates, stored as glycogen in muscles and the liver.
Strategic timing is crucial: Consuming specific macronutrients at the right times—before, during, and after training—is vital for performance and recovery.
Electrolytes prevent cramping: Minerals like sodium, potassium, and magnesium, lost through sweat, must be replaced to maintain fluid balance and muscle function.
Protein aids muscle repair: Adequate protein intake is essential for repairing muscle damage incurred during training and accelerating recovery.
Female runners are at risk of iron deficiency: Due to factors like menstruation and foot-strike hemolysis, female distance runners need to monitor their iron levels closely.
Don't forget healthy fats: While not a primary race-day fuel, healthy fats from nuts, seeds, and avocados provide long-lasting energy and support hormone function.
Personalize your nutrition plan: Each runner's needs and tolerances are different, so practicing your fueling strategy during training is non-negotiable.

Macronutrients: The Foundation of a Marathon Diet

For a marathon runner, a well-structured diet built on a solid foundation of macronutrients is non-negotiable. These are the primary sources of energy that power your muscles and support recovery from intense training. The balance and timing of carbohydrates, proteins, and fats must be tailored to individual needs and training phases.

Carbohydrates: The Primary Fuel Source

Carbohydrates are the body's preferred and most efficient energy source for high-intensity, long-duration exercise. They are stored as glycogen in the liver and muscles, acting as a readily available fuel tank during a race. Adequate carbohydrate intake is crucial to prevent "hitting the wall," a term for severe fatigue caused by glycogen depletion.

Complex Carbohydrates: These should form the bulk of your daily intake, providing sustained energy. Examples include whole grains, legumes, and starchy vegetables.
Simple Carbohydrates: Fast-acting carbs like those found in gels, sports drinks, and fruit are essential for quick energy boosts before and during a race.

Protein: For Muscle Repair and Recovery

Protein is vital for repairing muscle tissue damaged during long runs and supporting training adaptations. While not a primary fuel source during the race itself, consistent protein intake is essential for recovery and injury prevention. Studies suggest that endurance athletes may need between 1.4 and 2.0 grams of protein per kilogram of body weight per day.

Lean meats, poultry, fish, eggs, and dairy are excellent sources of animal protein.
Plant-based options include tofu, tempeh, lentils, and beans.

Fats: A Long-Lasting Energy Reserve

Healthy fats are a dense energy source, particularly useful for slower, long-duration efforts when the body taps into fat stores for fuel. They also play a crucial role in hormone regulation, inflammation management, and vitamin absorption. Runners should prioritize sources of healthy, unsaturated fats such as avocados, nuts, seeds, and olive oil.

Micronutrients and Hydration: The Critical Details

While macros provide the bulk of energy, specific vitamins, minerals, and proper hydration are the critical elements that fine-tune a runner's performance and prevent setbacks.

Essential Vitamins and Minerals

Iron: Crucial for producing hemoglobin, which transports oxygen to your muscles. Female and high-mileage runners are at a higher risk of iron deficiency due to increased losses from sweat, hemolysis, and menstruation.
Vitamin D: Aids in calcium absorption and bone health, which is critical for runners facing high-impact stress. It is also linked to muscle function.
B-Complex Vitamins: These are central to energy metabolism, helping the body convert food into energy.
Antioxidants (Vitamins C & E): Intensive training increases oxidative stress. Antioxidants help protect cells from damage.

The Importance of Hydration and Electrolytes

Adequate hydration is paramount for performance and is more complex than just drinking water. Electrolytes, which are minerals lost through sweat, must be replaced to maintain fluid balance, nerve function, and muscle contractions.

Sodium: The most significant electrolyte lost in sweat. Insufficient sodium can lead to cramps and, in severe cases, hyponatremia.
Potassium, Calcium, and Magnesium: These minerals also play key roles in muscle function and overall cellular health.

Nutrient Timing for Marathon Training

Your nutritional strategy must adapt to your training schedule. A marathon runner's food and hydration intake changes significantly throughout the day and in the days surrounding their race.

Pre-Run: A meal 2-4 hours before a long run should be rich in carbohydrates and moderate in protein, with low fiber to avoid digestive upset. A small, carb-heavy snack can be taken 30-60 minutes before the start for a final energy top-up.
During-Run: For runs over 60-90 minutes, consuming 30-90 grams of carbohydrates per hour from gels, chews, or sports drinks is recommended to maintain energy levels. Regular sips of fluid with electrolytes are also crucial.
Post-Run: The recovery window post-exercise is prime for refueling. Consuming a carbohydrate and protein-rich meal or snack within 60 minutes helps replenish glycogen stores and repair muscles. A ratio of approximately 3:1 carbs to protein is often recommended.

Comparison Table: Nutrient Needs Pre-, During, and Post-Marathon


Nutrient Category	Pre-Marathon (3-4 hours prior)	During Marathon	Post-Marathon (within 60 min)
Carbohydrates	High-carb meal (e.g., porridge, bagel), easy to digest.	Quick-acting, simple carbs (gels, sports drinks), 30-90g/hr.	High-carb intake to replenish glycogen stores (1-1.2g/kg/hr).
Protein	Moderate amount to aid satiety and blood sugar control.	Generally not needed, prioritize carbs for energy.	High-quality protein (20-25g) to initiate muscle repair.
Fats	Low to moderate to avoid digestive issues.	Minimal to none, as they slow digestion.	Healthy fats are important for overall recovery later.
Hydration	~16-24 oz fluid, mostly water.	~400-800ml fluid per hour with electrolytes.	Replenish fluids lost (125-150% of weight lost).
Electrolytes	Start well-hydrated, supplement if needed.	Consistent intake via sports drinks/tabs, especially sodium.	Continue replacing losses, add salty foods.

Conclusion

Running a marathon is a demanding feat that requires a comprehensive and strategic approach to nutrition. What nutrients does a marathon runner need goes beyond basic fuel and involves a precise balancing act of carbohydrates, proteins, healthy fats, and crucial micronutrients like electrolytes, iron, and Vitamin D. A personalized plan covering pre-race carb-loading, during-race fueling with fast-acting carbs and electrolytes, and strategic post-race recovery nutrition is essential for success. By listening to your body and practicing your nutrition strategy in training, you can ensure you have the energy and resources to cross the finish line feeling strong. Consulting a sports dietitian can help fine-tune a plan to meet your individual needs and performance goals.

Frequently Asked Questions

For endurance events, runners should aim for 30 to 90 grams of carbohydrates per hour to prevent glycogen depletion and maintain energy levels. The specific amount depends on individual factors like pace, body weight, and tolerance.

Protein should be consumed regularly throughout the day and is especially important in the recovery window within 60 minutes after a run. A snack or meal with 20-25g of high-quality protein combined with carbohydrates helps with muscle repair.

Electrolytes can be consumed through sports drinks, gels with added electrolytes, or specialized electrolyte tablets and chews. Regular intake is recommended, especially sodium, to replace minerals lost in sweat.

Marathon runners have an increased risk of iron deficiency due to higher losses from sweat, foot-strike hemolysis (damage to red blood cells), and, for women, menstruation. Iron is crucial for oxygen transport to working muscles.

A pre-race breakfast should be a low-fiber, carbohydrate-rich meal eaten 2-4 hours before the start. Familiar options like porridge, a bagel, or pancakes topped with fruit are good choices, avoiding high-fat or high-protein foods that digest slowly.

While individual needs vary, a general guideline is to consume 400-800ml of fluid per hour during running, especially when it is hot. It is important to match intake to sweat rate and include electrolytes.

Carb-loading is a strategy to maximize your glycogen stores in the days leading up to a marathon by increasing carbohydrate intake. For events longer than 90 minutes, it can improve performance, and should be practiced during training.