Carb Loading

What, Why, & How-to

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Carb Loading for Runners

That one pre-race pasta dinner isn’t going to cut it if we’re looking to fully lock and load our carbohydrate stores for race day. Let’s take a few steps back and carb load the week before our race, paying particular attention to the 2 to 3 days leading up to our race for the greatest success.

Ever hit the wall with 10k to go? Carb loading allows us to store more energy to prevent that wall face plant & performance-limiting fatigue. Carb loading may be one of the easiest parts of marathon training but is also one of the most commonly overlooked pieces of marathon preparation. It is beneficial to carb load for any race lasting over 90 – 120 minutes.

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What is carb loading?

We can store carbohydrates in the form of glycogen in our muscles. These glycogen stores allow us to stock up to about 2 hours of energy for racing. As we train, we deplete and replete our glycogen stores, yet most runners never fully restore their full capacity of glycogen. Carb loading involves increasing our carbohydrate intake over the days prior to racing. The excess carbohydrate consumed is combined with water to create glycogen, aka the storage form of carbohydrates in our muscles. The goal of carb-loading is to completely fill our glycogen stores. A well-trained runner can store up around 500 gm of carbohydrates as glycogen.

Glycogen is 1 gram of carbohydrate + 3 – 4 grams of water. As we increase carbohydrates, we also want to increase fluid intake. A full carb load also helps with hydration by providing us extra fluid stores for race day.

Why should I carb load?

Endurance performance is enhanced by high carbohydrate availability. We ensure this by fully stocking our glycogen stores + taking fuel during our race. Depletion of glycogen stores causes fatigue, decreased performance, decreased work rate, increased perceived exertion, and lack of coordination.

The higher the intensity, the more we rely on carbohydrates for energy. If we’re looking to PR and work to our highest ability until the end of the race, we want to start with our glycogen stores fully loaded. When we race a marathon, over 75% of the fuel we use is coming from carbohydrates. The only way to ensure adequate carbohydrate availability is by completing a full carb load and taking fuel consistently throughout the race.

Who can carb load?

Studies show both men and women can adequately carb load if adequate carbohydrates are eaten. Research shows adequate carbohydrates to fully load glycogen stores are 10 – 12 gm/kg x 2 days or 8 gm/kg x 3 days.

How-to Carb Load

It is quite simple. The week before your race as your mileage tapers, keep your nutrition fairly similar to if you were running a higher mileage week. This will slowly begin the carb load. Then, we take a strategic approach 2 – 3 days out from the race. Use the calculator below to determine how many carbs you need to eat. You pick 2 or 3 days for the carb load.


  • If you think you will have trouble increasing your carbs, pick 3 days.
  • If the calculator is recommending >800 grams of carbs per day, try a 3+ day carb load, or reach out for personalized carb loading advice that may be more appropriate for you & your race.”

Now that you know how many carbs you need to eat, download this free How-to Carb Load guide for step-by-step advice to execute this easily.

Tips for carb loading

  • Use carbohydrate foods you are familiar eating. Do not choose a bunch of new-to-you foods.
  • Focus on high carbohydrate foods, not high fat foods. For example, choose a baked potato instead of French fries, a bagel instead of a donut, pretzels instead of chips, or juice instead of a milkshake.
  • Choose lower fiber foods. As we increase volume, higher fiber foods can quickly add up to too much fiber leaving too much roughage in the GI tract and increasing the risk of GI issues on race day.
  • Spread your nutrition out throughout the day so you are not forcing too much food at once.
  • Consider making your biggest meal the day before your race at lunchtime and eat a lighter dinner for an early morning race.
  • Focus on hydration. An adequate carb load needs extra fluids.
  • Consider drinking some of your calories. Use sports drinks, juice, lemonade, or other sugar sweetened beverages.
  • You do NOT need to deplete carbohydrate stores before carb loading. This is old, outdated science that will only contribute to unnecessary stress during the taper.
  • Do NOT get on the scale. The point of carb loading is to stock the body with extra carbs & fluid. If seeing the scale increase will bother you, stay off the scale.
  • The most common reason carb loading doesn’t work is because we don’t eat enough carbs. Learn what you need and get after it!

Prefer to listen to your carb loading advice? Tune into Episode: 10 – Carb Loading from Fuel for the Sole for more information.

Don’t skimp on the carb load if you’re looking to crush your next race!

Disclaimer: this is for education & informational purposes only. It’s always best to consult with a sports dietitian for personalized nutrition recommendations. If you have questions on your calculated results, reach out to Featherstone Nutrition to have a personalized 3 Day Carb Load guide completed for you within 10 business days.