Most Endurance Athletes Are Carb Loading Wrong. Here’s What the Science Actually Says

Carb loading sounds pretty simple.

Eat a big plate of pasta the night before your race and you're good to go.

At least that's how many runners, cyclists, triathletes, and other endurance athletes approach it.

Unfortunately, that's not really carb loading.

While athletes generally understand that carbohydrates are important before a long race, many significantly underestimate how much carbohydrate is actually required to maximize muscle glycogen stores.

A pasta dinner might be part of your carb loading strategy.

But carb loading is a process, not a meal.

If you're preparing for a marathon, ultramarathon, long cycling event, triathlon, or another endurance race lasting several hours, getting it right could make a meaningful difference late in the race.

Let's look at what the science actually says.

TLDR: How Should Endurance Athletes Carb Load?

Most endurance athletes do not need to completely reinvent their diet before a race. But if you're truly trying to maximize glycogen stores, eating a little extra pasta the night before probably isn't enough.

• Carb loading is generally most useful for endurance events lasting longer than about 90 minutes.
• Current sports nutrition recommendations commonly suggest approximately 10 to 12 grams of carbohydrate per kilogram of body weight per day for the final 36 to 48 hours before an important endurance event.
• For a 160 pound athlete, that works out to roughly 725 to 870 grams of carbohydrate per day.
• You do not need to completely deplete your glycogen stores before carb loading.
• Reducing training volume while increasing carbohydrate intake helps maximize glycogen storage.
• High fiber foods, large amounts of fat, and excessive protein can make hitting carbohydrate targets unnecessarily difficult.
• Liquid carbohydrates and easily digested foods can make aggressive carb loading much easier.
• Carb loading will usually increase body weight because glycogen is stored with additional water. That is expected and potentially beneficial.
• Do not wait until the night before your race to suddenly eat an enormous amount of unfamiliar food.
• Practice your carb loading strategy before an important race just like you practice your race day fueling.

The biggest mistake isn't that endurance athletes don't eat carbohydrates.

It's that most don't eat nearly enough carbohydrates to actually call it carb loading.

What Is Carb Loading?

Carbohydrate loading is a nutritional strategy designed to maximize the amount of glycogen stored within your muscles before prolonged endurance exercise.

When you eat carbohydrates, they are broken down primarily into glucose.

Some glucose is immediately used for energy.

Some is stored as glycogen in your liver and muscles.

During endurance exercise, your muscles rely heavily on these carbohydrate stores for energy, particularly as intensity increases.

The problem is that glycogen storage is limited.

You can store enormous amounts of energy as body fat.

Carbohydrate storage is considerably smaller.

That makes glycogen a valuable and limited fuel source during prolonged endurance exercise.

Carb loading attempts to start the race with those stores as full as reasonably possible.

Why Glycogen Matters So Much for Endurance Athletes

Anyone who has run a marathon has probably heard about "hitting the wall."

Cyclists might call it bonking.

Whatever you call it, glycogen depletion is one of the major contributors.

As muscle glycogen becomes depleted, maintaining a high exercise intensity becomes increasingly difficult.

Your body can use fat for energy, and trained endurance athletes are very good at doing so.

But fat metabolism cannot provide ATP at the same rate as carbohydrate metabolism.

That's why the harder you're working, the more important carbohydrates generally become.

Starting an endurance event with elevated glycogen stores essentially gives you a larger carbohydrate fuel tank.

Research has consistently demonstrated that carbohydrate loading can increase muscle glycogen concentrations and improve endurance performance, particularly during events lasting longer than approximately 90 minutes.

The Classic Pasta Dinner Isn't Really Carb Loading

Here's where most athletes go wrong.

They eat normally all week.

Then the night before the race they go to an Italian restaurant and order a giant bowl of pasta.

Maybe some bread.

Maybe dessert.

And they call that carb loading.

That's certainly a carbohydrate rich dinner.

But physiologically, that's not the same thing as carbohydrate loading.

True glycogen supercompensation generally requires a sustained period of high carbohydrate availability combined with reduced training.

Modern carb loading protocols typically involve approximately 36 to 48 hours of very high carbohydrate intake before an important endurance event.

That means your carb loading strategy should probably start roughly two days before the race, not at dinner the night before.

How Many Carbs Do You Actually Need?

This is the number that surprises most athletes.

Current sports nutrition recommendations commonly suggest:

10 to 12 grams of carbohydrate per kilogram of body weight per day

during the final 36 to 48 hours before prolonged endurance competition.

That is a lot of carbohydrate.

A 130 pound athlete weighs approximately 59 kilograms.

That means roughly:

590 to 710 grams of carbohydrate per day.

A 160 pound athlete weighs approximately 73 kilograms.

That's roughly:

730 to 875 grams per day.

A 190 pound athlete weighs approximately 86 kilograms.

That's approximately:

860 to 1,030 grams per day.

Now compare that with a typical plate of pasta.

Two cups of cooked spaghetti contains roughly 85 grams of carbohydrate.

That's a decent amount.

But if you're a 160 pound athlete targeting around 800 grams of carbohydrate for the day, you'd theoretically need the carbohydrate equivalent of almost 19 cups of cooked spaghetti.

Obviously, I am not recommending you eat 19 cups of pasta.

The point is simple:

A pasta dinner isn't going to get the job done by itself.

This Is Why Carb Loading Feels Like So Much Food

When athletes first calculate their actual carbohydrate target, the reaction is usually something along the lines of:

"There's no way I can eat that much."

And if you're trying to get 700, 800, or 900 grams of carbohydrate exclusively from oatmeal, brown rice, sweet potatoes, vegetables, and whole grain bread, they're probably right.

You'd feel stuffed.

This is one situation where the way endurance athletes normally think about a healthy diet may actually work against them.

For most of the year, high fiber, minimally processed foods are great.

During an aggressive 36 to 48 hour carbohydrate load?

You probably want to temporarily prioritize carbohydrate density and digestibility.

Stop Trying to Make Your Carb Load Perfectly "Clean"

This is something I think endurance athletes unnecessarily struggle with.

Race week isn't the time to win an award for eating the most vegetables.

Your goal during the final 36 to 48 hours isn't to create the world's healthiest diet.

Your goal is to:

• Maximize glycogen.
• Keep your stomach comfortable.
• Show up fueled.

Foods such as white rice, pasta, bagels, pancakes, cereal, pretzels, white bread, juice, sports drinks, bananas, applesauce, jam, honey, and low fiber carbohydrate products can make it significantly easier to reach high carbohydrate targets.

You aren't going to develop a nutrient deficiency because you ate white bread for two days.

There is a time for brown rice.

There is also a time for a bagel covered in jam.

Race week might be the latter.

Fiber Can Become Your Enemy

Imagine trying to consume 800 grams of carbohydrates primarily through oatmeal, beans, brown rice, whole grains, vegetables, and high fiber fruit.

Your gastrointestinal system might stage a rebellion before you ever reach the starting line.

Fiber increases food volume and can contribute to bloating, gas, and bowel movements.

That doesn't mean you need to eliminate fiber completely.

But reducing fiber during the final day or two before a long race can make it easier to increase carbohydrate intake while potentially decreasing gastrointestinal problems on race morning.

For athletes with sensitive stomachs, this can be especially helpful.

Don't Fill Up on Fat and Protein

Protein is important.

Fat is important.

Neither needs to disappear during a carb load.

But here's the problem:

They take up room.

If you're trying to consume 700 or more grams of carbohydrate in a day while simultaneously eating your normal amount of fat, protein, fiber, and vegetables, your total calorie intake can become enormous.

Instead, carbohydrate intake should temporarily become the priority.

Keep protein reasonable.

Reduce unnecessary dietary fat.

Then let carbohydrate make up a much larger percentage of your total intake.

You're not abandoning good nutrition.

You're adjusting your nutrition for a very specific performance goal.

Liquid Carbohydrates Are Your Friend

This might be one of the easiest ways to hit aggressive carbohydrate targets.

Drinking carbohydrates is often easier than eating them.

• Fruit juice
• Sports drinks
• Carbohydrate drink mixes
• Smoothies
• Other carbohydrate containing beverages

A bottle containing 60 to 100 grams of carbohydrate can be considerably easier to consume than another giant plate of food.

This becomes particularly useful later in the day when you're already full but still have 200 grams of carbohydrate left to hit your target.

That's also where Simply Good Supplements GlycoFuel can fit in really well.

GlycoFuel was designed as a simple carbohydrate fuel for endurance athletes, making it easier to add meaningful carbohydrate intake without forcing down another full meal. It can be used during training and racing, but it can also be a practical tool during a carb load when your appetite starts becoming the limiting factor.

If you're trying to reach 700, 800, or even 900 grams of carbohydrate in a day, being able to drink part of that total can make the process much easier.

And because carb loading should be practiced before race week, GlycoFuel can also be incorporated during long training sessions so you can figure out exactly how your stomach responds before it matters.

The point isn't that you need a supplement to carb load.

You don't.

But liquid carbohydrates can make a high carbohydrate target much easier to reach.

You Don't Need the Old School Depletion Protocol

Older carb loading strategies were considerably more complicated.

Athletes would perform exhaustive exercise to deplete glycogen.

Then they'd eat a low carbohydrate diet.

Then they'd dramatically increase carbohydrate intake.

The idea was essentially to empty the tank before overfilling it.

Fortunately, modern research suggests you don't need to put yourself through that.

A taper combined with high carbohydrate intake appears sufficient to substantially increase glycogen stores.

That's good news.

The last thing you need several days before a marathon is an exhausting glycogen depletion workout.

You've already done the training.

Now recover and fuel.

Your Taper Is Part of Carb Loading

This is an overlooked part of the equation.

Carb loading isn't just:

Eat more carbs.

It's:

Eat more carbohydrates while dramatically reducing the amount of glycogen you're burning through training.

That's one reason carb loading works so well alongside a taper.

Training volume decreases.

Carbohydrate intake increases.

Your muscles continue storing glycogen while using less of it.

That's how you arrive at race morning with maximized glycogen availability.

So don't panic when your training volume drops while your food intake increases.

That's exactly what you're trying to accomplish.

Yes, You're Probably Going to Gain Weight

This one freaks runners out.

You start carb loading.

You step on the scale.

You're two or three pounds heavier.

And suddenly you think you've ruined your race.

You haven't.

Glycogen is stored with water.

Common estimates suggest each gram of glycogen may be stored alongside approximately 3 grams of water.

If you substantially increase muscle glycogen, body weight should increase.

That's not fat gain.

That's fuel and water.

And both are going to be useful during your race.

I'd actually be more suspicious of a carb load where your weight didn't change at all.

A temporary increase in body weight before a long endurance race is not something you need to fix.

You're filling the tank.

Don't Forget the Carbs You're Eating During the Race

Carb loading doesn't eliminate the need for race fueling.

This is another misconception.

You cannot store enough glycogen to fuel an entire marathon or ultramarathon at a competitive intensity.

The goal is to:

Start with maximal glycogen stores.

Then:

Preserve those stores by consuming carbohydrates during the race.

For prolonged endurance events, modern sports nutrition recommendations often fall somewhere around 60 to 90 grams of carbohydrate per hour, depending on event duration, intensity, athlete tolerance, and the types of carbohydrates being consumed.

Highly trained athletes with well trained gastrointestinal systems may consume even more.

This is another place where GlycoFuel can fit naturally into an endurance fueling strategy because you can use the same carbohydrate source in training that you plan to rely on during racing.

The key is not to suddenly jump from 30 grams per hour in training to 90 grams per hour on race day.

Train your gut just like you train your legs.

Gradually exposing your gastrointestinal system to your intended race day carbohydrate intake during long workouts can make higher carbohydrate intakes considerably more manageable.

Carb Loading Shouldn't Begin With an Eating Contest

There's a difference between carb loading and overeating.

You don't need to sit down and eat 300 grams of carbohydrate at dinner.

In fact, that's probably a great way to feel terrible.

Spread carbohydrate throughout the day.

For example:

• Breakfast
• Morning snack
• Lunch
• Afternoon snack
• Dinner
• Evening snack
• Carbohydrate containing drinks between meals

If your target is 800 grams for the day and you're awake for 16 hours, that's an average of about:

50 grams per hour.

Suddenly, the number doesn't seem quite as ridiculous.

A bagel with jam and juice could easily provide 100 grams.

A bowl of cereal with a banana could provide another 100.

Rice with lunch might provide 150.

A carbohydrate drink could provide 60 to 100.

Now you're getting somewhere.

What Might a Carb Loading Day Look Like?

Let's use a hypothetical 160 pound athlete.

At approximately 73 kilograms, a target of 10 grams per kilogram would equal roughly:

730 grams of carbohydrate.

Breakfast

Bagel with jam.
Banana.
Cereal with milk.
Orange juice.

Approximately 150 grams of carbohydrate.

Morning Snack

Pretzels.
Applesauce.
Sports drink.

Approximately 90 grams.

Lunch

White rice.
Small serving of lean protein.
Bread.
Fruit.
Juice.

Approximately 150 grams.

Afternoon

Carbohydrate drink or GlycoFuel.
Low fiber snack.

Approximately 100 grams.

Dinner

Pasta with a lower fat sauce.
Bread.
Sports drink.

Approximately 150 grams.

Evening Snack

Cereal.
Banana.
Honey.

Approximately 90 grams.

Total: Approximately 730 grams of carbohydrate.

Notice something?

This doesn't require one insane meal.

It requires eating carbohydrates consistently throughout the entire day.

That's what carb loading actually looks like.

Practice Your Carb Load Before Race Week

This might be the most important practical recommendation in this article.

Don't experiment with 800 grams of carbohydrate for the first time two days before your goal marathon.

Practice it.

Pick a long training weekend.

Try a high carbohydrate day beforehand.

See what foods sit well.

See which drinks work.

Figure out how much fiber you can tolerate.

Figure out whether certain foods make you bloated.

See how your gastrointestinal system responds.

That's not glamorous sports nutrition.

But it's useful.

You practice your shoes.

You practice your race pace.

You practice your gels.

You should practice your pre race nutrition too.

Who Actually Needs to Carb Load?

Not everyone needs an aggressive carb load.

If you're running a 5K, you don't need 48 hours of 12 grams per kilogram of carbohydrate.

Your existing glycogen stores are more than sufficient.

Carb loading becomes more relevant as event duration increases.

It makes the most sense for events lasting approximately 90 minutes or longer, particularly when you're trying to maintain a relatively high intensity.

That includes:

• Marathons
• Ultramarathons
• Long trail races
• Triathlons
• Long cycling races
• Gravel races
• Long cross country skiing events
• Other prolonged endurance competitions

The longer and harder you're going, the more important carbohydrate availability becomes.

The Most Common Carb Loading Mistakes

Mistake #1: Starting Too Late

Dinner the night before isn't enough. Think approximately 36 to 48 hours.

Mistake #2: Not Eating Enough Carbohydrate

High carbohydrate and actual carbohydrate loading aren't necessarily the same thing.

Mistake #3: Eating Too Much Fiber

You're trying to store glycogen, not set a personal record for vegetable consumption.

Mistake #4: Eating Too Much Fat

High fat foods can quickly drive calories up while making it harder to reach carbohydrate targets.

Mistake #5: Eating Enormous Meals

Spread carbohydrates throughout the day instead.

Mistake #6: Being Afraid of Temporary Weight Gain

Glycogen brings water with it. That's part of the process.

Mistake #7: Trying It for the First Time Before Your Biggest Race

Practice your carb load.

Mistake #8: Assuming Carb Loading Replaces Race Fueling

It doesn't. Start full and continue fueling.

The Bottom Line

Most endurance athletes aren't completely wrong about carb loading.

They're just not doing enough of it.

A giant bowl of pasta the night before your marathon is better than going into the race carbohydrate depleted.

But that's not really a complete carb loading strategy.

If you're preparing for an important endurance event lasting longer than approximately 90 minutes, the research suggests a more deliberate approach.

• Start approximately 36 to 48 hours before your race.
• Aim for roughly 10 to 12 grams of carbohydrate per kilogram of body weight per day if you're truly trying to maximize glycogen.
• Reduce excessive fiber and fat.
• Use easy to digest carbohydrate foods.
• Drink some of your carbohydrates if necessary.
• Expect your weight to increase slightly.
• Continue fueling during the race.
• Practice the entire strategy before race week.

If getting enough carbohydrate through food alone becomes difficult, GlycoFuel can be an easy way to add carbohydrate during both your carb load and your race day fueling plan without forcing down another full meal.

We spend months obsessing over mileage, workouts, shoes, heart rate, VO2 max, and race pace.

Then some of us show up to our biggest race of the year after eating one plate of spaghetti and call ourselves carb loaded.

Don't let nutrition be the part of your race preparation you leave to chance.

Do the training. Fill the tank. Then keep filling it while you race.

References

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