Marathon Nutrition 101: How to Eat for a Successful Race Day

Training for a marathon is one of the most grueling, resolve-testing physical challenges. With your sights set on the finish line, it’s easy to get tunnel vision and focus too much on your training and not enough on your nutrition.

Fortunately, this dietitian-guided article covers all the basics, so you know what to eat every step of the way.

Adjust Your Calories

Women adjusting her calories for marathon training

Training for a marathon demands a ton of energy. As you increase the amount of time you spend running, it’s vital to increase your calorie intake to meet your new training demands. New marathoners often make the mistake of thinking that monitoring their weight is an effective way to determine if they’re consuming enough calories. However, this is a common misconception.

If you’re training in a caloric deficit, you may experience a dip in performance and less-efficient recovery periods before you ever see the scale change. To avoid this common misstep, individualize your caloric intake based on your age, body composition, resting metabolic rate, training complexity and environmental training conditions.

Master Your Macros

To successfully fuel your marathon training and performance, you’ll need to understand how all three macronutrients play a role in your performance. Here’s a quick rundown.


whole-grain bread rich in carbohydrates

Muscle glycogen is the body’s primary fuel source during endurance activities, such as running, swimming and bicycling. Excess dietary carbohydrates are stored in the muscle tissue as glycogen, which the body breaks down into glucose when it needs more energy. Keeping glycogen stores high is necessary to maintain energy levels during long runs.

Carbohydrates come in two forms: simple carbs and complex carbs. The body digests simple carbs much faster than complex carbs. One example of a simple carb is sugar, whether it’s found in fruit or ultra-processed sweets. Complex carbs are starchy foods that can either be refined (e.g., flour and pasta) or unrefined (e.g., whole grains and veggies). The majority of your diet should consist of complex carbohydrates.

Carbohydrates should contribute to 55 to 65 % of your total calories. That said, the amount you need depends mainly on the duration and intensity of your training. We’ll dive deeper into this breakdown in the following sections to help you understand how to calculate the right amount of carbs.


protein-rich meat

Running utilizes hundreds of muscles in your body, which demands a ton of energy. Dietary protein intake is essential for rebuilding and repairing muscle tissue as it breaks down during endurance training. Protein consumption is vital if you want to prevent muscle loss and build a stronger stride.

Proteins should account for roughly 10 to 15% of your total calorie consumption. That said, individual protein requirements can vary based on your weight, training intensity and training duration. However, generally speaking, endurance runners need between 1.0 to 1.6 grams of protein per kilogram of body weight.

Amino acids are the building blocks of protein and come in two forms: nonessential and essential. Essential amino acids are consumed through natural food sources in your diet. Eat a variety of different protein-rich foods derived from animals and plants to ensure that you’re getting enough essential amino acids in your diet.


avocados rich in healthy fats

Dietary fat can be utilized as an energy source during long runs and is necessary for numerous vital bodily functions. Fats are categorized into three groups: trans fats, saturated fats and unsaturated fats. Keep your diet high in unsaturated fatty acids and heart-healthy fats for optimal performance.

Foods high in unsaturated fatty acids include oils, fish, avocados, nuts, nut butters and seeds. Omega-3 fatty acids help decrease inflammation and increase oxygen delivery throughout the body, improving performance. Salmon, walnuts, flaxseeds and chia seeds are all great sources of omega-3’s!

Fat should account for roughly 20 to 30% of your total calorie consumption. Since dietary fats aren’t directly utilized for energy during running or used to synthesize muscle tissue, there’s no specific fat intake recommendation for runners.

Training Nutrition

women preparing for a marathon

In the months leading up to race day, you’ll want to eat to optimize your performance gains, while also observing what works best for your body and adapting accordingly. Here’s how to do that.

Follow a Periodized Nutrition Program

Align your nutrition plan with your pre-race performance goals. This strategy is known as periodized nutrition, and it’s an essential component of any marathon nutrition program.

To learn more about periodized nutrition, follow this link.

Time Out Your Intake

With nutrition, timing is just as important as quantity. Eating too far from or too close to a rigorous run can leave you feeling sluggish and cause running fatigue. Eat a balanced meal no sooner than 90 minutes before training. After your run, reach for a quick source of carbs to help refill the glycogen in your muscles.

To maximize your training benefits, consistently eat protein throughout the day. Aim to eat about 30 grams of protein at each meal with a few protein-rich snacks in between for full returns on your training investment.

Stay Hydrated

Staying hydrated is essential to help your body recover from training sessions. To estimate your fluid losses, weigh yourself before and after each training session. Then, drink at least 16 to 20 ounces of water for every pound lost during exercise. Track your water losses from session-to-session to ensure you lose no more than 2% of your total body weight.

Race Week Nutrition


Preparation for race day starts the week of the event. Here’s how to prepare when you’re approaching the starting gate.


Carbohydrate loading, aka carb-loading, is a tried-and-true method for improving race day performance. Carb-loading involves decreasing your activity and increasing your carb consumption in the days leading up to the race. Doing this causes your muscles to store unutilized carbs as glycogen, which can be tapped into for energy on race day, preventing you from hitting a wall.

To effectively carb-load, decrease your physical activity levels and increase your carb intake to 10 to 12 grams per kilogram of body weight per day in the 12 to 72 hours leading up to the race. In the 12 hours leading up to the race, slowly decrease the amount of food you’re eating, but keep it carb-heavy. Stick with carb-dense, high-glycemic foods low in fiber such as bread, rice, pasta and low-fiber fruit.

Race Day Nutrition

Breakfast before a marathon

From what you eat to when you eat it, everything counts come race day. Here’s how to maximize your performance.

Eat an Ideal Breakfast

Two to three hours before the race, eat a light meal high in simple carbs. Eating too close to the competition can cause a decrease in your blood glucose levels, which can negatively impact your performance.

Stay Hydrated

Proper hydration is essential for minimizing cramps and delivering energy to your cells! Drink two 8-ounce glasses of water at least two hours before the race.

During the race, be sure to drink enough fluid, so you don’t lose any more than 2% of your body weight. Also, make sure to increase or decrease the amount of fluid depending on the weather and climate, which may vary from the area you trained.

Keep Carbs On Hand

During the race, consume 30 to 60 grams of carbohydrates every hour after your first hour. Aim to consume a combination of simple carbs, such as both glucose and fructose-based foods. Sports gels, drinks and powders are also an option, as they’re easy to carry and consume in the middle of your run.

Post-Race Recovery

Eating post-race is essential for optimizing recovery, rebuilding muscle tissue and replenishing your glycogen stores. Your body’s ability to convert carbohydrates into muscle glycogen is highest 30 to 60 minutes after the race.

Consume 1.2 grams of carbohydrates per kilogram of body weight. Incorporating protein in a 1:3 ratio (protein-to-carbs) can also help increase the replenishment of glycogen. This meal can be a combination of simple and complex carbohydrates.


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written by

Kara Kash

Kara Kash