Carb Loading for Runners

Whether you’re looking for information on carb loading for marathon distances or a break down of how to carb load, this post walks you through it all.

runner on trail wearing backpack

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Table of Contents

  • What exactly is carb loading?
  •  Who may benefit from carb loading?
  • How far in advance should I start carb loading?
  • How many carbs should I eat?
  • What are some examples of carb loading foods?
  • Will I gain weight if I carb load?

If you have been in the running community for any amount of time, you have likely heard of runners “carb-loading” before a big competition.  Starting with the pasta parties that are thrown before middle school cross country meets, the idea that a large amount of carbs can provide great pre-race fuel has been popular for a while-and for good reason!

It is essential that the body has proper carbohydrate stores to provide energy during a race. That’s why the “pasta before marathon” idea evolved and carbo loading before a race. This is how to avoid hitting the wall in a marathon.

peanut butter and jelly

Research has shown that carbohydrate loading may improve endurance performance by 2-3%! That can translate to minutes, depending on how you look at it.

However, you may be confused on how exactly carb loading for runners works and whether it may benefit you. When should you carb load can be just as important as how you carb load.

What is Carb Loading?

Contrary to popular belief, carbohydrate loading is more than just eating a large bowl of pasta before a race.

plate of spaghetti with sauce and cheese

Carbohydrates are the body’s primary energy source during physical activity, especially as intensity increases. When we eat carbohydrates, they are stored as glycogen in our muscle and liver. Our liver can store up to 100 g (400 calories) of carbs, and our muscles can store up to 400 g (1600 calories) of carbs. This is enough energy to fuel about 2 hours of intense exercise.

Carb-loading is a strategy to maximize your energy availability by eating a high amount of carbohydrate, while decreasing your activity levels in the days before a race.

This strategy helps to ensure your glycogen stores are increased above their normal amount. However, not everyone equally benefits from carb-loading, which we will discuss in a minute. Those who are interested in keto and running are on the complete opposite end of the spectrum.

Essentially, carb loading before half marathon and carb loading before a marathon can both make a big difference. Here’s a sample idea of what to eat before long run.

Woman with sunglasses running ultramarathon

How To Carb Load

When breaking down how to carb load, you need to make sure you’re eating the proper amount of carbohydrates so your muscles can really store them. You’ve likely heard (and hopefully practiced) carbs before marathon races, so here’s how to strategically include them.

The most current recommendations for how many carbs to eat for carb loading are to consume 10-12 g/kg body weight of carbs per 24 hours during the carb-loading period.

For example, plugging numbers into this carb loading calculator, a person weighing 140 pounds (63.6 kg) would need to eat 636-763 g of carbs per day in the 36-48 hours leading up to their race.

That is a hefty amount, and usually takes some planning and pre-planning to do this, or working with a dietitian.

woman and man running on trail with mountains in the background

When To Carb Load

If you’re like many of my athletes, you’ve wondered when should you carb load? Certainly not for a shorter race and not something you only want to do the night before, but you don’t need to start too early either!

Carb loading for running doesn’t have to be overly complicated.

It used to be standard for athletes to carb-load for over a week before a competition. However, current research suggests that athletes should carb-load no earlier than 48 hours before a competition.

More recent research indicates that carb-loading can be completed 36-48 hours pre-race combined with a taper in training for 3-6 days. This is where high carb lunch ideas for runners comes in handy.

However, it’s still important that marathon runners are eating enough throughout their training. For more information, check out this sample long distance runners diet plan

It can also be helpful to refer to the performance plates for athletes, and modify from there. For carb loading, you’ll want to decrease veggies that take up room and maximize your carbohydrates. 

Carb Loading For a Half Marathon

When SHOULD you carb load, aka who benefits the most? Generally speaking, the longer the distance, the more the benefit.

The types of exercise that benefit the most from carb-loading are the types that are likely to deplete your muscle glycogen stores, including endurance running.

Research has shown that carb-loading may be most beneficial for those completing >90 minutes of moderate exercise. Therefore, carb loading before a half marathon may be helpful if you plan on running anytime above 90 minutes.

Marathon Carb Loading

Carb loading for marathon distances and beyond are more appropriate and beneficial than shorter races, as we’ve covered.

Similar to carb loading before a half marathon, carb loading for a marathon can be helpful and improve performance and decrease the perceived effort of exertion.

The main difference will be that while you may deplete glycogen stores during a half marathon, you may not. In the marathon distance, it’s almost certain that you will.

Hence, carb loading can be more widely relied upon, and the types of fuels you take during the marathon will also make a big difference.

You’ll likely need between 30-80 grams of carbohydrates per hour, to keep blood sugar stable, and prevent hitting the wall. These nutrition tips for marathon runners are helpful in determining more about that.

Best Foods for Carb Loading

There is an art to carb loading for running. It is important to choose foods that allow you to eat the right amount of carbs while avoiding GI issues.

Foods that are high in carbs while also being high in fat or protein may limit your ability to eat enough. Additionally, foods high in fiber may cause early fullness and gut problems.

This can be a little more challenging for those who eat a lot of fruits and veggies or follow a vegan runner diet.

This may seem confusing because we’re telling you to eat high carbohydrate foods, but carbohydrate foods are generally foods high in fiber.

So, what are we saying?

When talking about carbohydrates, there are two main types: simple carbohydrates and complex carbohydrates.

For the purposes of carb loading before a race, we want to stick to mostly simple carbohydrates with less fiber (white bread, white pasta, tortillas, certain fruits) because they will be easier to digest and less likely to cause bloating and discomfort.

Additionally, it is generally better to eat familiar foods in the days leading up to a race, which is same period in which you would be carb-loading.

So, what foods are best to eat for carb-loading? Foods that are familiar to you with high amounts of carbs and low amounts of fiber and fat are the most helpful.

Examples of carb loading foods may include rice, pasta, bread, cereal, potatoes, tortillas, fruits (including juices and smoothies), milk, and crackers.

different breads and carbohydrate foods

Here are some tips for successful carb-loading:

  • Practice to increase gut tolerance! Start with 5-7 g/kg per day and build up from there
  • Try eating smaller meals and snacks throughout the day rather than 3 large meals
  • Drink juice or milk with meals instead of water
  • Eat a serving of fruit with each meal
  • Choose refined grains over whole grains to lower the fiber content to settle your stomach (It helps if you have trained your gut to take in carbs during long runs!)

High Carb Snack Ideas

It will be difficult to meet your carbohydrate needs through 3 square meals, so this is where snacks will help.

Some easy-to-digest, high carb snack ideas include:

  • poptarts
  • fig newtons
  • pretzels
  • raisins and dried fruit
  • bananas
  • cereal
  • granola
  • graham crackers
  • applesauce
  • sports drinks
  • Adding tailwind or Skratch to water

Will Carb Loading Before a Race Make Me Gain Weight?

If you try carb-loading, you may notice a 1-2 kg weight gain, which translates to 2-4 lbs. This is completely normal.

The reason for this is because for every 1 gram of glycogen we store in our muscles, 2-3 g of water are held along with it to keep it stored and ready to use.

Therefore, the weight gain is a sign that your energy stores are full and ready to go for race day. This is also why people who start a low carbohydrate diet lose weight initially, it’s water weight. Once they start reintroducing carbohydrates back into their diets to the normal amounts, they usually regain that water weight as well.

It’s not extra fat that we put on our bodies.

More importantly, this is another example of why weight does not necessarily affect performance!

If helpful, it can be advantageous to work 1-1 with a dietitian when carb loading for a race.

Resources: 

  1. Academy of Nutrition and Dietetics, American College of Sports Medicine, and Dietitians of Canada. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501-528.
  2. Casazza, G. A., Tovar, A. P., Richardson, C. E., Cortez, A. N., & Davis, B. A. (2018). Energy availability, macronutrient intake, and nutritional supplementation for improving exercise performance in endurance athletes. Current Sports Medicine Reports, 17(9), 215-223.
  3. Hawley, J. A., Schabort, E. J., Noakes, T. D., & Dennis, S. C. (1997). Carbohydrate-loading and exercise performance: An update. Sports Medicine, 24(2), 73-81.  
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