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Carb Loading Before a Half Marathon

Amanda Wendorff

Whether you are a new runner looking to tackle a half marathon or a seasoned competitor, you've probably heard the term "carb loading" thrown around. What exactly is carb loading, and why should you care about it for your half marathon? In short, in longer races like half marathons and marathons, increasing your intake of carbohydrates ("carb loading") before a race can ensure that you have the fuel and energy necessary to race hard without experiencing the dreaded bonk. In this article, we're going to dive into the science, benefits, and practical tips of carb loading so you can run your best all the way to the finish line.

What You'll Learn From This Article

Before we dive into the nitty-gritty of carb loading, let's highlight some of the key concepts that will be covered in this article:

  • The various sources of fuel for long-distance running and why carbs are so important for half marathon success
  • How many carbs your body needs to complete a strong half marathon
  • The benefits of carb loading before a half marathon
  • Tips for implementing a smart carb load over multiple days before a race
  • Pitfalls to avoid when carbo loading before a half or full marathon

Now that you know what to expect, let's dig deep into the world of carb loading and why it's essential for your half marathon.

MOTTIV app users Kurt Lundqvist and his wife Maria Romano compete in a half marathon in Cocoa Beach, Florida!

Why Carbs Matter For Endurance Runners

To really appreciate the importance of carbohydrates in your running journey, let's break it down in simple terms.

When running, the body needs a steady supply of energy, especially for longer races like half marathons or marathons. This energy comes from different sources: fats, proteins, and carbohydrates. All of these macronutrients are important, but for the endurance athlete, carbohydrates are the superstar of the lineup. Why? Because the body is able to convert carbohydrates into energy very quickly and efficiently, which is useful for demanding activities like running.

How The Body Uses Carbohydrates

Let's walk through how it works: first, you consume carbohydrates, whether as part of your daily eating or via sports nutrition products like gels or sports drinks. Through a series of metabolic processes, these carbohydrates get converted into glucose, a type of sugar that the body can use very quickly as a fuel source. This glucose will circulate in your bloodstream and provide energy for the activities you are doing at the moment: thinking, breathing, moving, etc.

When the body has an ample supply of glucose - like right after you eat a meal, it will store the excess glucose in your muscle and liver cells in the form of glycogen. When needed, glycogen can be quickly accessed and converted to energy to keep you moving forward. In simple terms, the more glycogen that is stored in the body, the more energy is available to propel you along the race course.

The Lowdown on Carb Loading

Now that we've got the basics down, let's talk about why carb loading in the days leading up to the race is so essential.

The main goal of carb loading is to make sure your body is loaded up on glycogen before the starting gun goes off. This is important because, in the process of racing a half marathon, your body will burn through a huge number of carbohydrates - much more than you could replace with sports nutrition like gels or electrolyte drinks.

Carb loading is like the pit stop where your race car gets fueled up before the big race. With a full tank of glycogen, your muscles have a readily available and easily accessible energy source, making sure you don't run out of gas during your half marathon. It's like having your own personal energy reserve. It can be a game changer!

Carbs take many forms, including fruit, potatoes, rice, pasta, bread, beans, and corn!

How Many Carbs Do You Burn in a Half Marathon?

To really get a feel for the importance of having an energy reserve of glycogen, let's look at some numbers to see just how many carbohydrates the average runner is burning through during a half marathon.

Of course, every runner is different, and the rate at which you burn through carbohydrates is dependent on many things, including how hard you are running, your metabolism, your size, and more. Estimates show, however, that running at a relatively high intensity, such as during a half marathon, could burn through 125 grams of carbohydrates, or even more, per hour.

What does that number mean? Well, it's equivalent to 500 calories of carbohydrates. Your average sports gel is about 100 calories and 25 grams of carbs. If you were to try to replace all the glucose you are burning during a half marathon, you may need as many as five gels per hour -- a Herculean task that may lead to some serious upset stomach!

This is where glycogen stores and carb loading come into the picture.

Why Carb Loading Matters for Half Marathons

Many runners know all about "bonking," or hitting the wall - a very unpleasant experience where your energy levels plummet, and your race day takes a nosedive. This happens when the body reaches a state of carb depletion or runs out of carbs to use for fuel. You want to avoid this situation!

However, as we've seen, the logistics of consuming enough sports food during a race to match your calorie burn can be tricky. That's where your body's glycogen stores come to the rescue.

Glycogen acts as your energy savings account, storing carbs for when you need them most. It's like having a secret stash of energy to tap into during your race. That stash of energy is built up through carb loading. What you eat in the days leading up to your half marathon can make the difference between a strong finish and a painful limp to the finish line.

The Power of Glycogen Storage

To grasp the importance of glycogen storage, let's talk numbers. On average, male runners can store about 15 grams of glycogen per kilogram of body weight, while women can store around 10 grams per kilogram. For a 175-pound male, that works out to about 1200 grams of carbohydrates that can be stored as glycogen. Each gram of carbohydrate is equivalent to four calories, so that means our 175-pound male could store up to 4800 calories. A 130-pound female, in comparison, can store up to around 600 grams of carbohydrates, or 1400 calories. That's a lot of spare energy!

These glycogen stores serve as a safety net, bridging the gap between the carbs you consume and those you burn during a half marathon. When your body needs an extra kick of energy, it can quickly convert glycogen into glucose, your muscles' preferred fuel.

The Basics of Carb Loading

The best way to ensure that you have a full tank of glycogen reserves is through increasing your carbohydrate intake in the two to three days prior to your half marathon. Here are some tips for an ideal carb loading strategy:

Spread Carb Loading Over Multiple Meals

Rather than gorging yourself at a pasta dinner the night before a race, think of carb loading as a gradual process. Start eating more carbs in the two or three days before your race, increasing the amount of calories coming from carbs gradually.

Carb loading over several meals offers a few key benefits:

  • Gradual replenishment: By steadily increasing your carb intake with each meal, you top up your glycogen stores without overwhelming your body.
  • Avoids discomfort: Scarfing down a massive, carb-heavy meal can lead to feeling uncomfortably full or sluggish. Gradual loading minimizes this risk.
  • Sustained energy: Spacing out your carb loading ensures a steady stream of energy in the days leading up to your race, especially when you have other tasks like travel and race prep to tackle.

One of the star meals during carbohydrate loading is the brunch or breakfast you enjoy the day before your half marathon. This meal should be packed with carbs to maximize your glycogen stores. Think pancakes, potatoes, or toast, all of which are carb-rich delights. It's a good idea to have this meal after your pre-race run for the day to ensure your body stores as much glycogen as possible.

Stick to Familiar Foods and Keep it Simple.

Be careful not to use carb loading as an excuse to indulge in low-quality foods, as this might make you feel sluggish and uncomfortable during your race. Cinnamon rolls may have a lot of carbohydrates, but they are probably a better choice for after the race. Similarly, avoid new foods that your system is not familiar with. Stomach upset before a half marathon is no fun!

Consider incorporating these carb-rich but basic foods into your carb loading:

  • Pasta
  • Bagels
  • Rice
  • Quinoa
  • Pancakes
  • Potatoes
  • Farro
  • Oats
  • Bread

The Closer the Race Gets, The More Boring Your Meals Should Be

As race day approaches, consider shifting towards lower-residue, easy-to-digest foods with little fiber. For your dinner the night before the race, keep it bland - think white rice, grilled chicken, or white pasta - things that are unlikely to cause gut issues.

Also, keep this meal a little lighter - your pre-race dinner should satisfy your hunger without making you feel stuffed. You don't want to go to bed with a full stomach, which can disrupt your sleep and affect your race performance.

Don't Stress About Weight

As you load up on carbs, your cells will retain water, resulting in temporary weight gain. In fact, for every gram of stored glycogen, there are four grams of water stored along with it. Don't worry; this won't negatively affect your race performance, and in fact, it will help you arrive at the start line well-hydrated.

Race Day: Carb-Loading Continues

On the day of your half marathon, your breakfast takes center stage. Assuming you didn't go for a run after your pre-race dinner, your glycogen stores should be close to full, so think of breakfast as your final top-up of carbs before the race. Aim for 2 to 3 grams of carbs per kilogram of body weight from foods that you have tested before training runs.

Some good pre-race breakfast ideas include:

  • A bagel and almond butter
  • Oats with berries
  • Toast with honey

Of course, don't forget hydration during this meal! A bottle with some sports drink is a good way to get a few extra carbohydrates into the system while also making sure you are hydrated.

FAQ for the Runner Planning a Pre-Half Marathon Carb Load

Q: What is carb loading?

A: Carb loading, also known as carbohydrate loading, is a strategy used by endurance athletes to maximize the storage of glycogen in the muscles and liver before an event such as a marathon or half marathon.

Q: Why is carb loading important for runners?

A: Carb loading is important for runners because it can help increase glycogen stores in the muscles, which can provide additional energy during a long race such as a marathon or half marathon.

Q: How do I start carb loading before a half marathon?

A: To start carb loading before a half marathon, begin increasing your carbohydrate intake several days before the race, aiming for around 3-5 grams of carbs for every kilogram of body weight per day.

Q: Is it necessary to carb load before a marathon or half marathon?

A: Carb loading before a marathon or half marathon is not strictly necessary for everyone, but it may benefit some runners in endurance events lasting longer than 90 minutes.

Q: Can I include fat and protein in my carb loading plan?

A: While the focus of carb loading is on carbohydrates, it's still important to include some fat and protein in your meals and snacks leading up to a race for overall balanced nutrition.

Q: What do I need to know about carb loading for a marathon?

A: For carb loading before a marathon, it's important to plan ahead, gradually increase carbohydrate intake in the days leading up to the race, and focus on easily digestible, low-fiber foods.

Q: Will carb loading allow me to run my best in a half marathon?

A: Carb loading can help ensure optimal glycogen stores and provide additional energy during a half marathon, potentially allowing you to run at your best performance level.

Q: What if I run out of glycogen during a race?

A: If you run out of glycogen during a race due to inadequate carb intake, you may experience fatigue, difficulty maintaining pace, and reduced performance, highlighting the importance of proper carb loading.


In a nutshell, carb loading is a key factor in optimizing half marathon performance by ensuring that you start the race with fully charged glycogen stores. By starting carb loading early, making smart food choices, and following the carb-loading tips provided in this article, you'll set yourself up for a stellar race day. Remember, the longer and faster the race, the more carbs you need, so plan your carb loading with care. When you cross the finish line triumphantly, you'll be glad you did.

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Amanda Wendorff

| Author

Amanda Wendorff is a professional triathlete, focusing on the 70.3 and 140.6 Ironman distances. In the last several years she’s competed in multiple gravel bike races. Top Achievements: Top 3 Ironman Ireland and Ironman 70.3 Coquimbo, Multiple time top-5 finisher, 3rd Overall at Moran 166 Gravel Race in Michigan, Age group podium at Gravel Worlds, Big Sugar, and Ned Gravel in first year of gravel racing.

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