Carbo Loading For A Marathon: What You Should Know

Carbo Loading For A Marathon: What You Should Know

If you’ve been searching for advice on carbo-loading for a marathon, you’ve come to the right place.

Let’s begin with what carbohydrates are.

Carbohydrates have a bad reputation, not only in general but with runners as well. And it’s easy to see why. Carbs–bread, pasta, potatoes, beer, etc.–are heavy. You feel stuffed after eating doughy sandwiches, bowls of pasta, or drinking even a single beer (I was always more of a whiskey man myself, but that’s not the point). It’s only been in recent years–literally within the last decade–that the benefits of adding carbs to your diet have been understood. While some runners still choose to limit their intake for good reason, carbs are especially helpful to marathon runners

Why is Carbo Loading Necessary for Marathon Runners? 

When carbs are stored in the body, they become glycogen (glucose), which helps fuel the body during long runs. Of course, you are still consuming heavy carbs, which means that if you overdo it, you’ll be fueled but lethargic and slow. When properly balanced, carbs will provide energy that will keep you running longer and up to 13.4% faster. Keeping your glycogen levels will help you avoid hitting the wall, or that point at which your glycogen levels are depleted, leaving you suddenly exhausted and fatigued

What is Carbo Loading?

Carbo loading is exactly what it sounds like–taking on more carbs in your diet than you normally would. Or to put it another way, carbo loading means loading up on carbs. 

Simple enough, right?

In mathematical terms, to carbo load is to consume roughly 7-10 grams of carbs per kilogram (2.2 pounds) of your body weight. Now, we’re not all math people–I’m certainly not–so you have two options. Download a calorie counter, which is quite simple, or you can alter your diet more intuitively. Add minor carb-sources like juice and certain fruits to your diet here and there over the course of a few days. 

This is substantially more carbs than runners are used to consuming, but it will help build up extra glycogen. Use fiber to help keep you regular, but don’t overdo it. 

By the day of your marathon, 85% to 95% of your calories should be carbs–approximately 600 grams a day. 

Check out the video below for an even simpler explanation.

The Right Marathons 

You shouldn’t be carbo-loading for all marathons though. 5ks and 10ks are comparatively brief compared to marathons, ultra marathons, and triathlons–meaning you won’t be depleting your glycogen levels during these runs. Carbo-loading for a marathon is only effective in those that last 90 minutes or more because your natural glycogen levels tend to get depleted after 90 minutes of intense exertion. 

The Right Carbs

In general, you want to have carbs with little or no added fats. Here are some examples:

  • Whole wheat pasta with tomato sauce (no cream sauces)
  • Plain baked potato
  • Rice
  • Beans
  • Vegetables: beets, corn, oats, quinoa
  • Fruits: bananas, apples, mangos, dried dates, raisins, goji berries
  • Oatmeal (with berries or a few slices of the fruits listed above)
  • Yogurt
  • Milk
  • Whole grains
  • Salt-free tortillas
  • Waffles
  • Pancakes with maple syrup (no butter)
  • Bagels

When Should You Carbo Load? 

Like anything else, practice makes perfect. In the weeks leading up to your marathon, you’ll undoubtedly be training, using at least one practice endurance run a week to simulate the marathon. That run will likely be three to four hours. Take on extra carbs a few days before that run. You will either overload, causing you to feel bloated and lethargic during this practice run, or you’ll consume too few carbs, and you’ll hit the wall. Either way, you’ll feel a specific form of lethargy that will tell you how you need to modify the carbo load. Once you find a sweet spot, continue to use it. Eat the same carbs at the same time of day. Make sure that when the day of the marathon comes, you follow the schedule accordingly so your body is prepared for the carbo load and knows what do with it. 

Begin your earnest carbo load two to three days before the marathon. 

Also, check out the video below to learn how to do it right by avoiding doing it wrong.

The Different Ways You Can Be Carbo Loading for a Marathon


Your three to four-hour marathon simulation runs should stop three to four weeks before the actual marathon. You’ll begin tapering runs (example below) around that time. In taper runs, you’ll carefully reduce the volume of the miles you run leading up to the marathon.

For example:

Let’s say your final week of long runs accumulates to 40 miles. From there, decrease your running distance by eight to 12 miles over the next four weeks.

First week: 32 miles

Second week: 24 miles

Third week: 16 miles

Fourth week: 8 miles

During this time, your diet is changing as well. Your body will rely on carbs rather than calories. You’ll need three to five grams of carbs per pound of body weight. You’ll also be reducing the fat intake to lessen the slight weight gain (two to four pounds) that may happen as you carbo load. By reducing the amount of physical training while continuing to carbo load, you’ll be increasing your glycogen storage, readying it for the big marathon blow-out. 

If tapering isn’t for you, there are two other options.

Six-day Protocol

This method is based on depleting your glycogen reserves six days before the marathon. This may sound insane, but by keeping the glycogen levels low prior to the marathon, your body will become more fuel-efficient. After glycogen depleting exercises such as empty-stomach runs or fartleks, you would continue to carbo load (4.5 grams per pound) while also consuming low-fat foods. The glycogen-depleted runs will potentially increase your endurance for the marathon. This is because your body will be accustomed to the low levels and will still be able to function without it. During marathons, your glycogen levels will deplete, so it makes sense. It won’t be easy or pleasant, but marathons aren’t exactly sipping mai tais in the shade next to Warren Zevon. 

Rapid Loading

For whatever reason, you decided to wait until the night before it was due to write your term paper. We’ve all done it. In Rapid Loading, you’re carbo-loading 24 hours before the big day. First, you’ll need to do a glycogen-depleting exercise the day before the marathon. Following this exercise, you’ll eat high-carb meals of five to six grams of carbs per pound. That means you’ll need to reduce your fat and protein for that day. 

Glycogen-Depleting Exercises

If you’ve decided that the Six-day Protocol or Rapid Loading regimens are for you, then you’ll need to do glycogen-depleting exercises. Eat low carbs between runs–focus on protein and fat to fill your stomach while keeping glycogen levels low. 

Tempo Runs

Continuous movement at a hard-comfortable pace for 25-30 minutes. Or, this method:

  1. Two to three-mile warm-up at a comfortable pace.
  2. Five to six miles at a comfortably hard pace.
  3. Two to three-mile cooldown run at a comfortable pace.

Check out our article on tempo runs for more information.

Fartlek Runs

Fartleks are intense speed-play runs that keep your muscles in a constant state of flux. If you’re using fartleks for glycogen-depleting marathon training, you should be running at a pace that you would if you were running a 10k marathon. 

  1. Two to three-mile warm-up
  2. Five minutes at your fastest pace
  3. Two minutes at a comfortable pace
  4. Three minutes fastest pace
  5. Two minutes comfortable pace
  6. Two minutes fastest pace
  7. One minute comfortable pace
  8. One minute fastest pace
  9. Five minute comfortable pace
  10. Repeat Fartlek again.
  11. Cooldown run of one or two miles.

Two Runs a Day

The aftermentioned tempo run done twice in a day. We suggest running in the early morning, allowing the afternoon for your muscles to heal but still remain malleable for the second run in the late afternoon or early evening

Empty-Stomach Runs

Your normal run, just rescheduled first thing in the morning, when your stomach is empty. The night before, eat a low-carb meal at 5 PM and nothing else after. 

The Morning of the Marathon

End on a calm, reasonable note. Only consume 150 grams of carbs before the marathon. That could be a bagel and a cup of vanilla yogurt, or decent energy drinks like Skratch Labs Sport Hydration Mix or Nuun Immunity.  

And there you have it: everything you need to know about carbo-loading for a marathon.

Preparing for a marathon isn’t easy. It’s grueling as all hell.

But it’s worth it.

Let us know what you think in the comments below.


  1. NY Times
  2. This Runner’s Recipes
  3. Run to the Finish