How to Carb Load for a Marathon: Maximize Your Performance

How to Carb Load for a Marathon? Carb loading is a crucial strategy for marathon runners aiming to optimize their performance and energy levels during a race. 

This technique helps improve endurance by increasing glycogen stores in the muscles. In this detailed guide, you’ll learn the fundamentals of carb loading for a marathon and half marathon, the timing and intake recommendations, and the right foods to consume for optimal results.

Carb Loading Basics

carb load marathon

Aim of Carb Loading

Carbohydrate loading, or simply carb loading, is a nutrition strategy that involves increasing carbohydrate intake in the days leading up to a long-endurance sports event. The purpose is to maximize glycogen stores in muscles and liver and thereby optimize energy levels on race day. Optimal nutrition for marathons is vital to maintain endurance throughout the race.

Rationale for Carb Loading

Glycogen is the stored form of glucose, which provides energy for endurance events such as marathons. By increasing carbohydrates before a race, runners can prevent their glycogen stores from depleting as quickly, helping maintain consistent energy levels and reduce the chances of “hitting the wall” during a race. Carb loading is only effective for endurance events lasting longer than 90 minutes.

Ideal Timing for Carb Loading

Since carb loading is a gradual process aimed at increasing glycogen stores, it is recommended to start increasing carbohydrate intake around 2.5-3 days before the race.

How to Carb Load

Carb loading should be tailored according to the specific race distance, either a full marathon or a half marathon, as their nutrition demands vary.

Carb Loading for Full Marathon

Carb Intake in Grams and Percentage

A full marathon requires higher carbohydrate intake during the carb-loading phase. The recommended carb consumption is 70% to 90% of the total daily calories. Aim for a carb intake of around 6-10 grams per kilogram of body weight.


Carb loading for a full marathon usually takes approximately 2.5-3 days before the race. This timeframe allows runners to maximize their glycogen stores, ultimately benefitting their performance.

Carb Loading for Half Marathon

Carb Intake in Grams and Percentage

Carb loading for a half marathon, though not as much as for a full marathon, is still essential. The carbohydrate intake ranges from 60% to 65% of the total daily calories. Aim for a carb intake of around 4-6 grams per kilogram of body weight.


The carb-loading duration for a half marathon is generally 2-3 days before the race.

Foods to Focus On

Good Sources of Carbohydrates

When carb loading, it’s essential to consume high-quality carbs that are easily digestible. Good sources of carbohydrates include:

  • Rice
  • Pasta
  • Bread
  • Cereal
  • Potatoes
  • Fruit

Foods to Avoid

High Fiber Foods

High-fiber foods such as legumes, whole grains, nuts, and some fruits may cause gastrointestinal distress for some people during the carb-loading phase. It is recommended to reduce these foods’ consumption to prevent digestive issues before the race.

High Fat Foods

High-fat foods can hinder the carb-loading process by slowing down the absorption of carbohydrates. Avoid consuming excessive amounts of fatty foods such as fried foods, full-fat dairy products, and fatty meats.

Carb Intake During Marathon

Importance of In-Race Fueling

Consistent carbohydrate intake during the marathon is essential to keep energy levels steady and maintain performance. Fueling for shorter runs, such as a half marathon, is also necessary but at a lower rate than a full marathon.

Recommended Carb Intake

During a marathon, endurance athletes should consume around 30-60 grams of carbohydrates per hour. This can be achieved through a combination of sports drinks, gels, chews, or other forms of easily digestible carbohydrates.

Common Carb Loading Mistakes


Carb loading doesn’t require excessive amounts of calories. Consuming too many calories, especially carbohydrates, can lead to weight gain and sluggishness. To avoid overeating, stick to the recommendations based on the race distance and your body weight.

Timing Mistakes

Proper timing is essential in carb loading. Starting too early or too late may compromise glycogen stores on race day. Following the recommended 2.5-3 days for carb loading ensures that your glycogen stores are at their optimal level.

Not Tailoring to Individual Needs

Individual needs and preferences vary, so tailor your carb-loading strategy to your specific requirements. Consider your body weight, fitness level, and personal experience to optimize your nutrition plan.

Frequently Asked Questions

Does carb loading work for events shorter than 90 minutes?

Carb loading is most effective for endurance events lasting more than 90 minutes. Shorter events don’t deplete glycogen stores as much, so the benefits of carb loading may be minimal.

Can carb loading cause stomach issues?

For some runners, increased carbohydrate intake can cause gastrointestinal upset. To avoid this, gradually increase your carb consumption and avoid high-fiber and high-fat foods during the carb-loading phase.

How to adjust carb intake based on body weight?

When carb loading, use the recommended carb intake grams per kilogram of body weight; 6-10 grams for a full marathon and 4-6 grams for a half marathon. Adjust the specific intake based on your personal needs and preferences.


Carb loading is a crucial tool for marathon and half marathon runners. By maximizing their glycogen stores, runners can maintain their energy levels and enhance their performance on race day.Following the recommendations in this guide, tailoring the strategy to individual needs, and ensuring their marathon distance knowledge is up to date will help runners optimize their nutrition for the race and achieve their goals—whether competing in one of the many diverse marathon formats or participating in a friendly half-marathon.