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Does Carb Loading Really Work?

July 11, 2024

Whether you’re an avid marathon-runner or a high school athlete, you’ve probably been told to carb load the night before your next big race or game.

But should all athletes be carb loading?

Before you reach for that extra slice of bread, we asked Christopher Barrett, RD, a registered dietitian at the Bone & Joint Institute, for answers.

Here’s what you need to know about carb loading to perform at your best.

Carb loading should take place over two days.

Carb loading, it turns out, is exactly what it sounds like.

“Carbohydrate loading is a strategy for endurance athletes that involves eating more carbohydrates over two days before a big event,” explains Barrett. “These carbs are stored as glycogen in your muscles and liver, which can boost performance by 2-3% and endurance by 15-25%.”

To properly carb load, you need to eat 10-12 grams of carbs per kilogram of body weight (or 4.54-5.45 grams per pound). While some research suggests that women might need slightly less, more studies are needed to confirm this.

> Related: How Much Fat and Carbs Should I Actually Be Eating?

But not all athletes need to carb load.

If you’re competing in an endurance event that exceeds 90 minutes, carb loading can be very beneficial.

“Not only can these extra carbohydrates reduce the likelihood of muscle glycogen depletion and hypoglycemia during the event, but they can also improve your endurance,” says Barrett.

But if you’re doing shorter distances or exercises that use short bursts of energy, it may not necessarily help your performance.

A few examples where carb loading is beneficial include:

• Attempting your personal best marathon.
• Powering up for a long bicycle race.
• Fueling your body for an intense Ironman® race or similar event.

“Carbohydrates help athletes meet the higher demands of intense competition,” explains Barrett. “Carb loading can help people perform their best when it matters the most.”

The best carbs to eat (and what to skip).

Not all carbohydrates are equal when it comes to powering through an endurance event.

Some foods you should include are:

• Rice.
• Pasta.
• Potatoes.
• Sports drinks.

Some foods to avoid, on the other hand, are:

• High-fiber cereals.
• Pasta with creamy sauces.
• High-fiber energy bars.
• Any new foods or drinks – don’t try this before an important race!

“If you have gastrointestinal issues, you may benefit from a lower fiber intake,” adds Barrett. “Select your carbohydrate sources carefully.”

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How and when to carb load correctly.

“A higher carbohydrate intake should not be the result of just eating more,” cautions Barrett. “Instead, emphasize your carbohydrate sources and reduce fat intake.”

This carb loading begins before your event, and here’s your timeline:

• 3 days to event: Typical intake
• 2 days to event: Increase carbs
• 1 day to event: Increase carbs
• Day of event: Typical high carbohydrate breakfast (3-4 hours before the start)

“Try your best to spread the carb intake across the day evenly and avoid consuming excessive portions before sleep since it may affect quality sleep and lead to GI issues,” adds Barrett.

The possible risks and downsides of carb loading.

If you select the wrong types of carbohydrates (e.g., excessive fiber or high fat), you may experience digestive issues on performance day.

You might also see the scale jump temporarily.

“Carb loading may lead to a short-term weight gain of 2-4 lbs, but don’t panic,” says Barrett. “This weight gain is from the extra glycogen and water stored in your muscle, which can be a good sign that your loading is on track.”

Need some help before race day? Ask an expert.

Your peak performance involves many things.

“If you need nutritional support, personal training or physical therapy before a major athletic event, reach out,” says Barrett. “We can help you perform at your best.”