A big bowl of tagliatelle alla bolognese against a bright blue background. Eating plenty of carbohydrates is one component of carb loading.

© Juan Moyano / Stocksy United

Does Carb Loading Actually Help You Perform Better?

Registered dietitians set the record straight.

By Brigitt EarleyNovember 21, 2023


There are many things we do to prepare for a workout, from filling up our water bottles to prioritizing a proper warm-up. But when you really kick things into high gear—like running a race or tackling a triathlon, for example—your body needs even more TLC to push itself further and harder. Enter carb loading.

Chances are good you’ve heard of carb loading before, but is it as simple as eating a bowl of pasta the night before a big fitness event? What actually happens when you carbo load, and does it really enhance your performance during a long bout of exercise? We chatted with registered dieticians to find out.

What Is Carb Loading?

“Carb loading is a performance nutrition strategy where you eat more carbohydrates leading up to exercise or an event, with the goal of enhancing your performance,” says Lexi Moriarty, RDN, a New Jersey-based registered dietician and certified specialist in sports dietetics at Fueled + Balanced Nutrition. “This helps to maximize the amount of glycogen, or stored energy, in the muscles and liver that's available for use during exercise.” 

When carb loading, athletes generally begin to increase their carbohydrate intake anywhere between one and three days prior to a race or event, adds Michelle Routhenstein, RD, a registered dietician and owner of Entirely Nourished

Who Should Try Carb Loading?

“Carbohydrate loading is most beneficial for endurance athletes who are competing for more than 90 minutes of time,” Routhenstein says. With that in mind, it’s especially helpful for endurance athletes participating in long-distance fitness events like running, cycling, swimming, and triathlons, adds Moriarty. 

“Carb loading will not necessarily make you faster, but it will allow you to maintain your pace longer without fatiguing due to the larger amount of glycogen energy available,” explains Alex Larson, RD, a Minnesota-based registered dietician who works with endurance athletes. “A well-trained athlete can store around 500 grams of carbohydrates as glycogen.” Studies suggest this kind of carb loading can provide a 2–3 percent performance increase for exercise longer than 90 minutes. In a long race, that might translate to crucial minutes off your time. 

When to Try Carbohydrate Loading

Carb loading can result in improved performance, you say? That sounds great to anyone with fitness goals, but carb loading isn’t for every situation. The practice is best if you’re gearing up for a long bout of exercise, such as a marathon, endurance swim, or long-distance cycling race—there’s typically no need to carb load before, say, a standard 30-minute jog.

Talk with your doctor or work with a nutritionist to ensure carb loading is right for you.

How Carb Loading Can Enhance Your Performance

Does carb loading guarantee an excellent performance? Of course not. There are many factors—health, weather, course conditions, you name it—that can affect your overall performance on race day. But for endurance athletes, carb loading can certainly help. It may:

1. Improve Race Times

When it comes to regular exercise—like a barre or cycling class, or even a 5K race—the amount of glycogen you have stored in your body should be enough to power you through. But when exercise exceeds 90 minutes and is particularly strenuous, your body may require extra fuel, which comes in the form of glycogen. When you strategically fuel up ahead of time with carbohydrates, you give your body a boost of extra glycogen stores, potentially resulting in a performance boost. 

2. Increase Stamina

Prolonged or intense exercise depletes the glycogen stores in your muscles and liver, which leads to fatigue. So the longer your glycogen stores last, the longer you may be able to maintain stamina and stave off mid-exercise fatigue. Since carb loading helps to top off glycogen stores, it may help you avoid total glycogen depletion by the end of a race. Speaking of which…

3. Aid in Recovery

If your body has leftover glycogen stores at the end of a race (or another endurance event), it can help make recovery more efficient, Moriarty says. Not to mention, replenishing glycogen stores is crucial for preparing the body for subsequent training sessions or competitions.

Types of Carbo Loading

There are a few different ways to go about carb loading, but each technique involves increasing the amount of carbs you eat while simultaneously decreasing activity levels in order to up your glycogen stores for improved performance. The longer the physical feat, the more time you need to spend carb loading, Larson says. (That means you likely want to start carb loading sooner in advance for an ultramarathon than, say, a half marathon.)

All that said, here are a few carb-loading approaches to keep in mind: 

One-Day Carb Loading

Arguably the most common type of carb loading among beginner or hobbyist athletes, the one-day carb loading approach is undeniably simple and great for shorter, less intense forms of exercise like a half marathon or triathlon. Here’s how it works: One day before the big event, athletes avoid exercise and consume a carb-rich diet. In order to carb load properly on a one-day schedule, you should aim to consume about 10–12 grams of carbohydrates per kilogram of body weight (or about 4.5 grams per pound), Routhenstein says. So for instance, a 150-pound person would want to consume about 675 grams of carbohydrates throughout the day before their race. 

Three-Day Carb Loading

During a classic three-day carb loading approach for longer distance events, athletes typically consume at least 70 percent of their standard daily calories in the form of carbohydrates while simultaneously drastically reducing physical activity. Experts, including Larson, generally recommend this approach for a full marathon or long-distance triathlon.

Six-Day Carb Loading

For distance events like an Ironman, some professionals recommend carb loading for as many as six days prior to the race. During a six-day program, athletes generally maintain exercise while consuming a low-carb diet (about 15 percent of their standard total calories) to decrease glycogen stores during those initial three days. (Some athletes opt for a more moderate carbohydrate consumption during these first few days—closer to 50 percent of their total calories.) Then, three days prior to the race, they boost carbohydrate consumption to as much as 70 percent of their total calories while simultaneously reducing physical activity. 

All that said, in most situations, “the six-day carb load isn't usually necessary unless you know you won't be able to meet your carb loading goals in the few days before your event,” Larson says.

How to Carb Load Correctly

Though the practice is relatively simple, there are a few factors that can improve your chances of correctly carb loading and, thus, reaping the most benefits:

Start at the Optimal Time

Aim to begin carb loading one to three days before the event—sometimes as many as six, especially if you’re undertaking a very long endurance race. As noted above, the longer your planned event, the further in advance you should start carb loading.

Consume the Appropriate Amount of Carbs

Generally, endurance athletes need 10–12 grams of carbohydrates per kilogram of bodyweight per day (or about 4.5 grams per pound). That total number of carbs should be divided across your typical meal pattern, Larson advises. So for example, if you eat three meals and three snacks per day, you’d aim to incorporate your total number of carbs across all six of those instances rather than trying to squeeze them in solely at dinnertime. 

Make Strategic Food Choices

“It's best to seek out foods that are lower in fat, lower in protein, and high in carbs,” Larson suggests. For example, doughnuts may have plenty of carbs, but you’re better off choosing a bagel before competing in a big endurance event.

Consider a Food Journal

If you’d feel comfortable doing so, Larson notes that using a food journal while you’re carb loading can help ensure you’re consuming plenty of carbohydrates to fuel your body in advance of the big day. There are plenty of online tools that can help with this, but you can also go the old-fashioned route with pen and paper or use the Notes app on your smartphone. 

A man carb loading with a plate of spaghetti.

Catherine Falls Commercial / Moment via Getty Images

Common Carb-Loading Mistakes

Trying nearly anything new comes with a learning curve. Fortunately, knowing some of the most common mistakes athletes make when carb loading can help you achieve success right out of the gate: 

1. Unstrategically Carb Loading

The most common carb-loading mistake athletes make is simply eating a large volume of food, rather than mapping out meals and snacks that come with the carbs you need. When athletes focus on quantity alone, they often don’t actually eat enough carbohydrates, Larson says. 

2. Hyper-Focusing on Carbs Alone

“Athletes may also make the common mistake to hyper-focus on carbohydrates during carb loading,” says Routhenstein. They might forget to consider things that can actually deter their performance goals, like not consuming enough protein or not staying adequately hydrated.

3. Introducing New Foods

Experts say it’s not advisable to introduce any new foods when you’re carb loading. Anything new and unusual can lead to digestive issues like an upset stomach or even an allergic reaction—two things you definitely don’t want to deal with before an important fitness event. 

4. Consuming Too Much Fat

Eating enough fat is crucial for fueling our bodies on a daily basis. But when you're practicing carb loading, it's possible to inadvertently consume too much fat in the process, which may lead to adverse results like gastrointestinal discomfort or impeded performance levels, Routhenstein says. For instance, experts recommend pairing your pre-race pasta with a light marinara sauce rather than a creamy alfredo to avoid any discomfort the next day.

5. Consuming Too Much Fiber

Eating too much fiber can also cause unwanted side effects like bloating, diarrhea, and general intestinal distress, Routhenstein says. Though high-fiber foods are vital parts of a healthy diet, the registered dietitians we spoke with generally recommend avoiding foods like beans and cruciferous veggies when carb-loading right before a big fitness event to avoid the risk of those not-so-fun side effects. 

6. Exercising Too Much

Oftentimes, athletes will exercise too much prior to their event, which limits the extent of glycogen, or stored carbohydrates, to be in effect—even with a high-carbohydrate diet, Routhenstein says.

7. Saving All of Their Carbs for Dinner

Don't jam-pack all your carbs in at dinnertime, Larson advises. Otherwise, you're going to be uncomfortably full. Rather, spread your carb intake across meals and snacks throughout the day.

8. Not Properly Hydrating

Staying hydrated is always important, but it’s especially crucial when you’re carb loading. The reason? Eating more carbohydrates requires more water for your body to properly absorb and digest them. Experts recommend drinking plenty of water and avoiding beverages like alcohol or those with caffeine (such as coffee, tea, and soda). That’s because these types of beverages can contribute to dehydration, which can negatively impact performance and negate the work you did carb loading. 

Foods to Eat and Avoid During Carbo Loading

For best results, it’s not enough to simply consume carb-rich foods. Consider this: Some candy bars and pastries contain more carbs than a serving of pasta, but the latter is the more optimal choice when prepping for a test of physical endurance. 

Here are a few foods to consider leaning into before the big day, as well as some to potentially limit:

Foods to Consider Prioritizing

Look for foods that are lower in fat, lower in protein, and high in carbs. Think wholesome carbs, fruit, and vegetables like the following:

  • Pasta

  • White bread

  • White rice

  • Smoothies, especially those containing bananas and citrus

  • Potatoes (peeled)

  • Applesauce

  • Pretzels

  • Low-fiber cereals

  • Fruit juices

Foods to Consider Avoiding

When you’re carb loading, experts recommend limiting high-fiber and high-fat foods, which might lead to gastrointestinal discomfort, including bloating and diarrhea on race day. These foods include:

  • Pizza

  • Candy

  • Pastries

  • Creamy sauces

  • Doughnuts

  • Energy bars

  • Ice cream

  • Chips

  • Beans

  • Cookies

  • French fries

  • Oatmeal

  • Cruciferous vegetables

  • Alcohol

  • Caffeine

The Takeaway

For endurance athletes, carb loading is an effective way to boost performance and even speed up the recovery process—and it only takes a few days to effectively do so. Plus, the formula is simple: increase carbs and decrease exercise. But don’t forget to pay attention to what you’re eating. Simply focusing on consumption isn’t the path to success—choosing wholesome carbohydrates is. And make sure to treat your body to the other things it needs to perform at an optimal level: plenty of fluids and a good night’s sleep are key, too. 

This content is for informational and educational purposes only and does not constitute individualized advice. It is not intended to replace professional medical evaluation, diagnosis, or treatment. Seek the advice of your physician for questions you may have regarding your health or a medical condition. If you are having a medical emergency, call your physician or 911 immediately.


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