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Carb Loading For a Marathon

Carb loading for a marathon is an important part of preparation and can actually improve performance by up to 2-3%! This post will review when to start carb loading for a marathon, how to do it, and what foods to include.

volunteer holding water bottle out during race

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If you have a big race coming up, it’s time to think about how you are going to prepare both physically (training) and from a fueling standpoint.

While we talk a lot about carb loading for runners, this post is going to discuss the importance of carb loading before a marathon, specifically, including when to start and how to do it.

Why To Carb Load

Carbohydrates (carbs) are one of the three macronutrients (along with protein and fat) that make up the calories in our foods, which therefore, provide our body with energy.

Carbs are the body’s preferred source of energy for both the brain and the muscles. The majority of your calories should be coming from carbs (~45-65%).

Carbs are the best foods for running stamina!

bins of gluten free carbs

Furthermore, if you carb load correctly, it takes some of the pressure off of needing to eat a ton on the day of the race.

Of course you still need to fuel appropriately beforehand and know what to eat during the marathon!

Runners may need more carbs than people who do not exercise regularly or intensely. Here are some of our picks for the best carbs for runners.

The exact amount of carbs a runner should eat is very individualized.

Even in our sample meal plan for marathon training, we don’t have a set number of carbs per runner since it varies.

The general rule of thumb for carb intake for active individuals is as follows:

Exercise LevelCarb Amounts Per Day
Light (low intensity)3-5g/kg of body weight
Moderate (~1 hour per day)5-7g/kg of body weight
High (endurance; 1-3 hours per day)6-10g/kg of body weight
Very high (>4-5 hours per day)8-12g/kg of body weight
Chart of carbohydrates needed for levels of activity.

For example, if a 150 lb. runner is aiming to get 3-5g of carbs per kg of body weight, that would look like 150lb./2.2 = 68kg X 3-5g = 205g-340g of carbs per day.

flours and oats can be gluten free foods

Carb foods include things like bread, pasta, rice, oats, potatoes, beans, and fruit. There are several options for gluten free carbs, too.

Carbohydrates provide the body with energy but also with good nutrients such as vitamins, minerals, and fiber. They are good for the digestive system and for heart health.

What is Carb Loading?

Carb loading involves an increased intake of carb-based foods before a long run or race while (usually) simultaneously decreasing exercise. This allows the carbs to be stored rather than used for energy. This is usually referred to as a “taper” period before a long run or race.

Research has shown that the human body can store approximately 90 minutes’ worth of carbs to be used as fuel for endurance exercise. This would be recommended for a full marathon, and for some people for half marathon nutrition, depending on their finishing time.

The main difference will be that while you may deplete glycogen stores during a half marathon, you also may not. In the marathon distance, it’s almost certain that you will deplete your glycogen stores, hence needing to properly carb load for the most benefits.

We have several other recommendations for what to eat before a marathon, too!

snacks in bowls, like popcorn, pretzels and chips

Carb Loading for a Marathon

There are different methods for carb loading for a marathon, including duration of the loading period as well as the amount of carbs to intake.

Here are two of the most common ways to carb load before a marathon.

  1. Taper 3-4 days before the race while increasing carbs to 8-12g/kg of body weight. For example, a 150-pound athlete would increase their carb intake to 545 – 818g of carbs per day (approx. 27-41 servings of carbs per day).
  • Taper 1-2 days before the race while increasing carbs to 10-12g/kg of body weight. For example, a 150-pound athlete would increase their carb intake to 682 – 818g of carbs per day (approx. 34-41 servings of carbs per day).
group of women running on trails

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

You do not need to gorge on a buffet of carbs for the entire 2-3 days for which you are carb-loading. Rather, increasing your carb intake slightly from your current intake will provide your body and muscles with the fuel they need.

The goal is NOT to feel uncomfortably full or miserable during the carb-loading period.

Be aware that carbs help retain water so during this time of increased carbs and decreased activity, you may gain a couple of pounds. Again, this is normal and will be used for energy during your race.

What are the Benefits of Carb Loading?

Carb loading, or increasing carb intake, helps to delay the onset of fatigue during the race. Going into a race well-fueled will help you to feel more energy and to have a better performance.

Carb loading has been found to improve performance by 2–3%!

One study even found that physical inactivity paired with a “high carb” (10g/kg of body weight) intake increased muscle glycogen stores by 90% after only one day.

girl sitting on boardwalk eating piece of fruit

So, this carb loading period does not have to be for a long time if you find it physically uncomfortable, or you don’t have several days to play around with the above-mentioned protocols.

If the race is longer than ~90 minutes, you’ll still need to fuel during the race, but carb loading will help you to feel ready to go at the start and prevent glycogen depletion early in the race.

In other words, it can help you conserve more energy and hopefully avoid hitting the wall!

Tips for Carb Loading Before a Marathon

Seeing as the above calculations are quite hard for most people to hit, I like to take the practical tips approach with a lot of my clients.

This is an example of the common saying,“nutrition is a science but it’s also an art”.

The science gives us these numbers, but the art is figuring out how the science applies to real life. And how it looks for each individual person.

pasta in baking dish

Here are some practical tips for carb loading in the days leading up to a marathon:

  • Increase carbs at every meal. 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. 
  • 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
  • Add more carb-foods to your snack repertoire and/or add a fruit to every snack
  • Pack your smoothies with fruits and juice
  • Mix tailwind in with your water
  • Include salty foods to help with hydration
  • Substitute water for more liquid carbs (sports drinks, milk, juice) – We love tart cherry juice!
  • Add honey or maple syrup to things like toast, oatmeal, smoothies or bananas. 1 Tbsp of honey is 17 grams of carbs!

For instance, if you typically have one slice of bread as part of your breakfast, consider upping that to two slices during your carb load.

If you typically have one serving of potatoes or rice at lunch, consider upping that to two, and so forth. Pasta is another great way to get more carbs in!

For snacks, if you typically snack on nuts in the afternoon, consider adding a piece of fruit or switching out the nuts for some pretzels and peanut butter.

Increasing salty foods, such as pretzels, goldfish crackers, soups, and jerky will help the body hold on to water, which is good for hydration before a marathon

bag of pretzels

Sample Menu/Plan for Carb Loading

Let’s take the first carb load method mentioned above and see how it breaks down in terms of food to provide a visual and concrete example. Check out this post on the best foods for carb loading for more ideas, too.

Carb load protocol:

  • Taper 3-4 days before the race while increasing carbs to 8-12g/kg of body weight.
  • For example, a 150-pound athlete would increase their carb intake to 545 – 818g of carbs per day (approx. 27-41 servings of carbs per day).

Sample Menu/Plan for 554g of carbs per day (~8g/kg for this 150-pound athlete)

Use this as a marathon carb loading calculator.

*(Grams listed are carbohydrates)

Breakfast (114g)  1 cup vanilla Greek yogurt (25g) 1 Tbsp. honey (17g) 2 slices wheat bread (31g) 1 cup berries (10g) 1 Tbsp. peanut butter (4g) 1 medium banana (27g)
Snack (73g)  1 cup pineapple (22g) 1 cup low fat milk (13g) 2 fig bars (38g)
Lunch (78g)  1 cup broccoli (6g) ½ cup carrots (6g) 3 oz. grilled chicken breast with breadcrumb coating (21g) 3/4 cup brown rice (24g) ½ cup black beans (20g) 1 Tbsp. parmesan cheese (1g)
Snack (115g)  38 pretzels (46g) 1 Tbsp. peanut butter (4g) 2 pouches fruit snacks (38g) 1 medium banana (27g)
Dinner (96g)  1 cup cooked broccoli (6g) 3 oz. roasted turkey breast with ½ cup gravy (6g) 1 cup pasta (42g) 1 Tbsp. parmesan cheese (1g) 1 slice chocolate cake (41g)
Snack (78g)  1 cup low fat milk (13g) 1 pear (27g) 2 fig bars (38g)

Carb Loading Questions

Do you need to carb load before a half marathon?

Maybe, but not necessarily! If your race is going to be longer than 90 minutes, carb loading may be beneficial.

Will I gain weight while carb loading?

Some people do gain weight when carb loading, but it’s important to note that it’s not fat gain, but instead, just water weight. This is because the extra carbs that we store as glycogen require water for storage in the muscle. When we deplete those carbs, the water goes too.

I don’t think I can eat that many carbs – can I still carb load?

Yes! The key is taking in more carbs than your body is used to. You can start on the moderate side with 5-7 g/kg body weight and slowly increase from there.

There you have it! Carb loading before a marathon is beneficial and it IS possible, with a little prep.

It just takes some pre-planning, some intention, and maybe only some small tweaks depending on your usual carb intake.

References:

Sports Nutrition: A Practice Manual for Professionals, 5th ed. (2012)

Podlogar T, Wallis GA. New Horizons in Carbohydrate Research and Application for Endurance Athletes. Sports Med. 2022 Dec;52(Suppl 1):5-23. doi: 10.1007/s40279-022-01757-1. Epub 2022 Sep 29. PMID: 36173597; PMCID: PMC9734239.

Vitale K, Getzin A. Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations. Nutrients. 2019; 11(6):1289. https://doi.org/10.3390/nu11061289

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