Endurance Athlete’s Guide to Carb Loading
If you've ever hung out with a group of endurance athletes before race day, then you’ve witnessed the phenomenon that is carb loading. They devour seemingly impossible quantities of white rice, pasta, bread, and potatoes, only to wash it down with sugary juice.
But why do endurance athletes carb load? And what’s the science behind it? Let’s get into it.
Quick Recap
- The purpose of carb loading is to maximize glycogen stores in the body before an endurance race.
- You should carb load for races over 90 minutes. There’s no need to carb load for shorter events.
- Consume 10-12 grams of carbohydrates per kilogram of body weight.
- Start loading 24-36 hours before the race. There’s no need for a depletion phase or longer carb load period.
- Choose fast-digesting carbs when loading (white rice, bread, pasta, clear juices). Avoid high-fiber and fatty foods, and any foods that might upset your stomach.
Why Do Athletes Carb Load?
The body stores energy from carbohydrates in the form of glycogen in the liver and muscles. When blood sugar levels run low, the body taps into its glycogen stores for energy. By consuming lots of carbs before race day, you ensure that your glycogen stores are full.
Think of it like the battery backup in a solar panel setup for your home. When the sun is shining (adequate blood sugar levels), the solar panels deliver energy to your home. But, when the sunlight levels go down or energy demands are higher than what the sun can deliver, it switches to the battery backup (glycogen stores).
If you want to stay powered, especially when energy demands are high, it’s best to start with a full battery. You won’t be able to power anything on an empty battery!
Don’t fully understand what glycogen is? Don’t worry. Read about it in our athlete's guide to carbohydrates.
How Much Glycogen Does the Body Store?
Most people can store approximately 500-800 grams of glycogen in the liver and muscles, which is enough stored energy for approximately 90-120 minutes of intense activity. During endurance races, even if you start off with full glycogen stores, you can still run out of energy before the race is over. This shows why it is important to fuel while you race so you don’t deplete your glycogen stores too quickly.
Read more in our fueling guide.
Pro Fact: Most glycogen is stored in the muscles. Some researchers believe the evolutionary reason for this is so muscles can access the energy quickly during our “fight or flight” reaction.
Do You Need to Carb Load for Every Race?
It is beneficial to carb load for any race that will last more than 90 minutes.
You do not need to carb load for races lasting less than 90 minutes. Your normal glycogen stores should be adequate, and carbohydrate loading will not make you any faster. Because carb loading can increase water retention, it may even be detrimental for certain non-endurance sports where increased body mass hinders performance.
What About Carb Loading before Intense Training?
Carb loading is typically reserved for races and not training. Why? Because, if you are frequently carb loading, it will be hard to maintain energy and nutrient balance.
How Many Carbohydrates to Eat When Loading?
To fully stock glycogen stores, you need to consume 10-12 grams of carbohydrates per kilogram of body weight in the 24-36 hours before the event.
If you do the math, you can see this is an insane amount of carbohydrates. A 65 kg man would need to consume 650-780 grams of carbs. To put that in perspective, it’s the equivalent of eating approximately 14 bagels.
When Should You Start Loading?
You should start carbohydrate loading at least 24 hours before the race. As long as it is timed well (see section below), this is enough to fully load glycogen stores.
No, You Don't Need to Load for 6 Days
Note that the “classic” carb loading protocol, developed by Scandinavian researchers in the 1960s, spanned 6 or 7 days. It had two phases:
- Depletion phase: This lasted 3-4 days. Athletes followed a low-carb diet and performed intense exercise to drastically reduce their glycogen levels. The idea was that fully depleting glycogen would prime the body to store more carbs during the loading phase.
- Loading phase: The remaining 3-4 days focused on tapering exercise and consuming a high-carbohydrate diet.
Modern research shows that this classic carbohydrate protocol is not necessary. Research shows there is no need to deplete your stores before loading. There is also no need to carb load for more than 24-36 hours, especially when it will interfere with training. A one-day protocol is adequate.
Timing Your Carbohydrate Intake During Loading
In general, you should spread your carbohydrate intake out throughout the loading period by constantly snacking throughout the day. This is easier on the body than trying to consume a huge amount of carbohydrates in one or two giant meals. However, there are some aspects of carb loading that you should time carefully.
Activation Exercise
Many athletes perform an activation ride or run on the day before the race. Because this activation ride will reduce glycogen stores, it doesn’t make sense to start carb loading beforehand.
Instead, do your activation exercise as early as possible on race day and start carb loading immediately afterward. This method is beneficial because evidence shows consuming carbohydrates after exercise increases glycogen synthesis in the muscles.
Pre-Race Dinner
Plan your dinner before race day so it is at least 2.5 hours before bedtime, and don’t stuff yourself. Otherwise, you might not be able to sleep well. Have a snack before going to sleep to top off stores.
Race Day Breakfast
While your muscle glycogen might be full from all the carb loading you did the day before, your liver stores may be low. This is because the body uses liver glycogen during the night. You’ll need to have a good breakfast to replenish those liver glycogen stores and keep fatigue at bay.
As a general rule, you should eat your breakfast 2-4 hours before the start of the race. However, this isn’t always possible, such as for early start times. In this case, consume 1 gram of carbohydrates per kilogram of body weight for each hour before the race.
For example, if you have just 2 hours before the race starts and weigh 65kg, you’d consume 130 grams of carbohydrates over the 2-hour period.
Pro Tip: Include fructose in your breakfast to maximize carbohydrate absorption. For example, you can top your white rice or semolina with jam, syrup or honey, or drink pulp-free juice alongside it.
What Should You Eat When Carb Loading?
Most of the carbohydrates we’ve been told are “healthy,” such as whole grain bread and sweet potatoes, are not good for carb loading. While they do contain carbohydrates that will fill your glycogen stores, they also contain a lot of fiber and fats.
Fiber and fat can take a while to make their way through the body. If any is left in your digestive tract on race day, it can cause stomach issues. For this reason, you should avoid fiber and fat for the 24 hours before the race.
Yes, that means your race-day oatmeal is off limits!
Also, note that fiber is an indigestible carbohydrate because it does not get broken down into glucose in the body, and thus fiber will not increase your glycogen stores.
Good Foods for Carb Loading
For carb loading, you want to focus on fast carbohydrates. This typically means refined sugar, white rice, and sugary foods. The list below has some good options.
Foods to Avoid when Loading
In addition to avoiding fiber and fat for 24 hours before the race, you should avoid spicy foods, carbonated drinks, undercooked meats, and unfamiliar foods. You don’t want to risk having stomach problems during the race!
Pro Tip: Test your carb loading plan during training so you know it will work for the race!
Tips for Packing in the Carbohydrates
One of the most common reasons that carb loading doesn’t work is because the athlete simply didn’t consume enough carbohydrates.
Yes, it can be challenging to consume the huge amount of carbs required to do carb loading successfully!
It will be much easier if you consume some of your carbohydrates in liquid form.
For example, a half liter of sweetened apple juice contains approximately 60 grams of carbohydrates. This is the same as 5 slices of white bread, but it’s easier to drink the juice than eat this much bread.
Do You Need to Drink More When Carb Loading?
Glycogen binds with water, so you will need to consume more fluids while carb loading. There’s no reason to go crazy drinking, though. It will fill up your stomach and make it harder to consume enough carbohydrates. Plus, you will constantly have to go to the bathroom, which in turn could make it harder to sleep.
Just keep a water bottle nearby, or consume some of your carbohydrates in liquid form, and you will be fine.