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How to Carb Load Before a Marathon

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Carb loading is one of the most well-known nutrition strategies used by top marathon athletes to improve performance during tough races. After all, endurance athletes are always striving to feel their best on race day, and the right nutrition strategy is a big factor. 

The eating the right food before a race can make the difference between a personal best and a does not finish! This article will cover what you need to know about carb loading to help you perform your best during your next marathon, and we'll even give you several strategies!

Pasta on a cutting board in preparation for carb loading

What is Carb-Loading?

When exercising, our bodies utilize stored carbohydrates to generate energy. Carbs are stored in our bodies in what is called glycogen. Glycogen stores are found in our muscles (80%) and livers (20%), and our body taps into these reserves during endurance events.

Carb loading involves increasing the muscle glycogen levels to above your normal amount. To do this, you'll need to adjust your diet to consume more carbs, and to prevent your body from burning the additional carbs, you'll need to reduce your training. More on carb loading strategies later

The nutritional strategy of carb loading works for sporting events that decrease glycogen stores, such as endurance running and cycling. 

Studies have shown that when endurance athletes use carb-loading correctly, they can reduce exhaustion and enhance exercise performance in activities that last longer than 90-minutes.

Runner preparing for a marathon

Carb-Loading Strategies Before a Marathon

Although strategies differ in intensity and duration, each of these common strategies use some form of the  "eat more carbohydrates and exercise less" philosophy. 

The strategies below have been developed and proven to be successful in the days leading up to a race.

Six-Day Carb Loading Strategies

There are two six-day carb loading strategies to choose between:

Classic Six-Day Carb Loading 

  • For the first 3-days of this strategy, continue exercising while eating a low-carb diet. Only about 15% of your total calories should come from carbs. This combination will decrease your glycogen levels.
  • On days four, five, and six, you'll need to eat a high-carb diet. Around 70% of your calories should come from carbs.
  • Exercise less on day four, and completely stop exercising on days five and six.

Modified Six-Day Carb Loading

  • With the modified strategy, you'll want to eat a medium-carb diet for the first three days. Around 50% of your calories should come from carbohydrates. 
  • On days four, five, and six, switch to a high-carb diet and consume 70% of your calories from carbs.
  • Exercise should be gradually decreased each day until you perform no exercise on day six.

Three-Day Carb Loading Strategies

Just like the six-day carb loading strategies, you have two plans to choose between:

Classic Three-Day Carb Loading

  • On the first day, you'll perform a strenuous exercise activity to the point that you are completely exhausted.
  • On days two and three, you won't exercise at all.
  • Eat a high-carb diet where 70% of the calories come form carbohydrates on days two and three.

Modified Three-Day Carb Loading

  • For days one, two, and three, you won't exercise.
  • Slowly increase the amount of carbs you eat over the 3 days. You'll need to eat approximately 4.5 grams of carbs per pound of body weight each day.

One-Day Carb Loading Strategy

  • The easiest strategy of all is to not exercise the day before your race and eat 4.5 grams of carbohydrates for each pound of body weight. 

Event Day Carb-Loading Strategy

  • Four hours before the race, eat around 1 to 4 grams of carbs per pound of body weight.
  • An hour before the race, eat 0.8 grams per pound.
  • If the idea of eating so close to the race doesn't work for you, you can always sip on a carbohydrate drink or consume an energy gel
Basket of healthy carbohydrates

How to Carb Load the Right Way

Whether you're new to carb-loading or you simply want to learn more, its important to learn how to do it right, otherwise it could negatively impact your race.

When to Carb Load

There are two key factors to consider when carb-loading to ensure you reap the benefits from this nutrition strategy:

  1. Carb-loading works best for exercise that exceeds 90-minutes without breaks.
  2. Only carb-load before endurance events or long training sessions. It's not necessary for speed training or weight training sessions.

Determine Your Carb Loading Strategy

As mentioned above, the carb loading strategies can be anywhere from one-to-six days. The simplest program to start with, if you are new to carb loading, is a one- or three-day program.

While training for the marathon, it's a best practice to try a few different strategies. Pay attention to how you feel and perform so you can determine which strategy works best for you.

Track your Carbohydrate Consumption

First, you'll need to know how many carbs you typically eat. You can do this by using the nutrition labels on food packaging, or by adding a food tracking app to your phone such as My Fitness Pal or Lose It.

Once you know how many grams of carbs you typically consume each day, divide the amount by your weight. Use this number to compare how you're doing with your recommended intake, and adjust as needed.

Increase Just the Carbs

You'll still want to watch your calories before race day. So, if you begin to increase your carbohydrate intake, you may need to decrease your fat intake.

Avoid foods that are high in both carbs and fat, such as pasta with creamy sauces or desserts and pastries.

Bowl of pasta for carb-loading

Best Foods to Eat Before a Marathon

It's always a good idea to eat the foods your body is used to eating. In other words, eat what you know. Now is not the time to start experimenting with new foods, as it could cause your stomach to rebel.  

Focus on high-carb, low-fat foods that contain moderate amounts of fiber.

Some of the most commonly recommended foods athletes use for carb-loading are smoothies, cereals, bread, and pasta. These items are high in carbs and low in fat. But let's take a deeper look at other great choices to eat in the week leading up to your race:

  • Cereal (low-fiber)
  • White bread
  • White pasta (avoid creamy sauces)
  • Fruit juice
  • Carbohydrate sports drinks
  • Low-fat and low-fiber energy bars
  • Lean protein (fish, poultry, fat-free dairy)
  • Smoothies
  • White rice
  • Potatoes with skins removed
  • Pretzels
  • Bananas, oranges, watermelon
  • Applesauce
Young girl looking through sport drink bottles

Common Carb Loading Mistakes

Carb loading can be a powerful tool for endurance athletes, but it's important to do it correctly. Here are a few common mistakes:

Carb Loading When it Isn't Needed - Carb loading is only effective when your exercise lasts for 90-minutes or longer. There's no benefit for shorter exercise sessions, speed training sessions, or weight training. 

Not Reducing Fat - Fat is part of healthy diet, but when it comes to carb loading, you need to cut back on your fat consumption. When you increase your carbs, you also increase your calories. If you don't stick to low-fat foods during this time, you could either gain weight or feel incredibly sluggish.

Eating Foods with High-Fiber Content - High-fiber foods can be detrimental when you're in the midst of your carb loading strategy. Just like fat, fiber forms part of a healthy diet, but too much fiber can result in stomach problems. While carb loading, opt for white bread or white pasta rather than the whole-grain alternatives. Other high-fiber foods, such as legumes, should also be avoided. 

Eating the Incorrect Amount of Carbohydrates - Experts recommend eating around 2.3 to 5.5 grams of carbs per pound of body weight each day. Eating too few carbs means you're not carb loading and you won't reap the benefits. On the other hand, eating too many carbs means you have consumed too many calories, and this can lead to weight gain.

Eating New Foods - As we mentioned above, now is not the time to start eating new foods, even if they are low-fat and high-carb. Unfamiliar foods have the potential to cause an upset stomach, which is something you definitely want to avoid . . . especially on the day of your race!

Continuing to Exercise - It's important to taper your exercise activities while carb loading. Depending on your strategy, you can still perform some relaxed exercises in the first few days. But on the final day, you shouldn't be exercising at all.

Not Drinking Enough - Certain types of drinks are incredibly beneficial when combined with carb loading. Some drinks, such as Gatorade, are excellent sources of liquid carbohydrates. The sodium in these drinks also helps to transport glucose through the body. So, it's important to combine carb loading with hydration to ensure you increase muscle glycogen stores before race day.

Eating Everything at Once - Some inexperienced runners try to carb load by eating all the carbs on the night before the race. Eating a heavy pasta meal the day before your race is not a good idea, as your body will not have enough time to store all the carbs. 

If you attempt to carb load like this, your blood glucose levels are likely to increase, as some carbs have the potential to increase blood sugar levels. You can consult the glycemic index of the food to see if this will happen. 

White board with FAQ's


Here's a couple commonly asked questions when it comes to carb loading:

Which Foods Should I avoid when I'm Carb Loading for a Marathon?

Food that are high in fat and fiber need to be avoided. Carbs with a high glycemic index (potential to increase blood glucose) should be skipped.

Some foods to avoid include creamy pasta sauces, muffins, cookies, chips, pizza, ice cream, and high-fiber cereals.

When is the Best Time to Start Carb Loading Before a Marathon?

Different strategies work for different people, but beginners should start carbohydrate loading 3 to 4 days before the race.

It's a best practice to try a few different carb-loading strategies before long training runs so you can get a feel for how your body responds and which strategy works best for you.

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