Do You Actually Need to Carb Load for Your Next Endurance Event?

October 22, 2025 •

4 min read

Research suggests that carb loading can improve performance in endurance events lasting over 90 minutes by up to 3%. However, this strategy is not universally necessary for all athletes, and its application depends on the type, duration, and intensity of the activity.

Quick Summary

This article explores the science behind carb loading, detailing which athletes genuinely benefit from the practice and for what types of events. It covers the modern approach to carb loading, provides practical advice on how to execute it, and identifies common mistakes to avoid for optimal performance without unnecessary discomfort.

Key Points

Event Duration Matters: Carb loading is most beneficial for endurance events lasting over 90 minutes; it's not necessary for shorter or less intense activities.
Maximize Glycogen Stores: The primary goal is to super-compensate muscle glycogen stores, which delays fatigue and boosts endurance performance.
Modern Method is Simpler: Forget depletion phases. The current best practice is to increase carbs for 1-3 days while tapering exercise, which is equally effective.
Prioritize Low-Fiber Carbs: During the loading phase, favor easy-to-digest, low-fiber carbs like white bread, rice, and pasta to prevent GI distress on race day.
Hydration is Key: Glycogen binds with water. You must increase fluid intake along with carbs to facilitate storage and stay properly hydrated.
Practice During Training: Always test your carb-loading strategy during long training runs or practice events to understand how your body reacts.
Avoid Common Pitfalls: Steer clear of trying new foods, loading too much fat/protein, or thinking one large pasta dinner will suffice.

The Science Behind Carb Loading: Filling the Glycogen Tank

Carbohydrate loading, or carb loading, is a nutritional strategy used by endurance athletes to maximize the storage of glycogen in their muscles and liver before a competition. Glycogen is the body's primary and most efficient fuel source during high-intensity exercise. Normally, our bodies hold a certain level of glycogen, but these stores can be depleted after about 90 minutes of continuous, intense activity, a phenomenon commonly known as "hitting the wall".

The goal of carb loading is to super-compensate these glycogen stores, effectively creating a larger 'fuel tank' for the body to draw upon during a prolonged event. By increasing carbohydrate intake while simultaneously reducing exercise volume (a process called tapering), athletes can significantly boost their available energy reserves. This strategy delays the onset of fatigue and helps maintain a higher intensity for a longer duration, which can be the difference between a new personal best and a frustrating slowdown.

Who Should Consider Carb Loading?

Not every athlete needs to follow a rigorous carb-loading protocol. For short-duration activities, like a 5K or a standard one-hour gym session, a normal, balanced diet provides sufficient glycogen. The benefits of carb loading are most pronounced for endurance athletes participating in events that last longer than 90 minutes.

Marathon Runners: A classic use case for carb loading. It helps runners get through the final miles strong and avoid severe fatigue.
Long-Distance Cyclists: Those tackling a long road race or endurance ride will benefit from maximized glycogen stores.
Triathletes: Competitors in half and full Ironman events require a massive energy supply over several hours, making carb loading essential.
Team Sport Athletes (Extended Tournaments): For back-to-back games in a basketball or soccer tournament, carb loading can ensure fuel stores are topped off for each successive competition.

The Modern Carb Loading Protocol

The old-school approach to carb loading involved a glycogen depletion phase with a very low-carb diet. Modern research has shown this is often unnecessary and can be stressful for the body. The contemporary method is much simpler and more effective, focusing on a strategic increase in carbohydrates in the 1-3 days leading up to the event.

Reduce Training Volume: As part of the taper, athletes significantly decrease their training intensity and duration in the days before the event.
Increase Carbohydrate Intake: Over the 1-3 days leading up to the race, increase your intake of carbohydrates to about 7-12 grams per kilogram of body weight per day.
Prioritize Low-Fiber Carbs: To avoid gastrointestinal distress on race day, focus on easy-to-digest, low-fiber carbohydrates. This means choosing white rice, white bread, and simple pasta over whole grains and excessive vegetables.
Stay Hydrated: Glycogen stores with water. Increasing carbohydrate intake requires a corresponding increase in fluid consumption to maximize storage and prevent dehydration. Expect a slight, temporary weight gain (1-2 kg) due to this water retention.

Comparison Table: To Carb Load or Not to Carb Load


Factor	Shorter Events (<90 min)	Longer Events (>90 min)
Need for Carb Loading?	Not necessary; a balanced diet is sufficient.	Highly recommended to maximize performance and delay fatigue.
Typical Training Fueling	Moderate-to-high carb intake, focus on quality.	High daily carb intake (8-12 g/kg/day during high volume).
Pre-Race Protocol	Normal pre-race meal 3-4 hours prior.	1-3 day carb load with increased carb intake and tapered training.
Best Carb Sources	Balanced mix of complex carbs and fiber.	Low-fiber, easily digestible carbohydrates to avoid GI issues.
Hydration Focus	Normal hydration strategy.	Consciously increase fluid intake to facilitate glycogen storage.
Risk of Bloating	Low.	Higher, especially with excessive fiber intake. Choose simple carbs.

Common Carb Loading Mistakes to Avoid

The Single Pasta Dinner: Many novice athletes believe a giant pasta dinner the night before is enough. This can lead to digestive issues and doesn't fully maximize glycogen stores. A multi-day approach is much more effective.
Ignoring Hydration: Water is crucial for storing glycogen. Without adequate fluids, the carb-loading process is inefficient. Increased water and electrolyte drinks are necessary.
Trying New Foods: Race week is not the time to experiment with new recipes or carb sources. Stick to familiar, tested foods to minimize the risk of an upset stomach.
Overeating Fat and Protein: Filling up on fat and protein leaves less room for the high volume of carbohydrates needed. While some lean protein is necessary for muscle recovery, the focus should shift to carbs.
Not Practicing: Just like training runs, practicing your carb-loading strategy on a few long training runs teaches your body how it will feel and react on race day.

The Final Carb Load: Race Morning Fueling

The final component of a successful fueling strategy is the pre-race meal. This should be consumed 2-4 hours before the event and focus on a final top-up of carbohydrates. Examples include oatmeal with banana, a bagel with jam, or toast. This meal ensures your liver glycogen stores, which are depleted overnight, are topped up for the start. For events lasting longer than 60 minutes, supplementing with gels or chews during the race is also vital to prevent energy depletion.

Conclusion: Tailor Your Strategy to Your Needs

In summary, the decision of whether you actually need to carb load depends on your event duration. For endurance races exceeding 90 minutes, it is a scientifically-proven strategy to maximize performance and delay fatigue. The modern approach is simple: taper training while increasing easy-to-digest carbs over 1-3 days, stay well-hydrated, and practice your fueling plan during training. For shorter, less intense activities, a normal, healthy diet is more than sufficient. By understanding the 'why' and 'how' of carb loading, athletes can make an informed decision to fuel their bodies for success without the pitfalls of an outdated approach. The American College of Sports Medicine provides additional guidelines on nutrition for athletic performance.

Frequently Asked Questions

No, carb loading is generally not necessary for a 5K. For shorter distances and less intense activities, your body's standard glycogen stores, maintained by a balanced diet, are sufficient.

You should start increasing your carbohydrate intake and tapering your training 1 to 3 days before your endurance event to effectively top off your glycogen stores.

If you don't carb load for an event lasting over 90 minutes, you risk depleting your glycogen stores and 'hitting the wall'—experiencing severe fatigue and a significant drop in performance.

Yes, but in moderation. The focus of your calorie intake should shift to carbohydrates, with reduced fat and protein intake, to maximize the room for glycogen storage without causing digestive issues.

Opt for low-fiber, easy-to-digest carbohydrates such as white pasta, white rice, peeled potatoes, white bread, fruit juices, and energy gels. Avoid high-fat and high-fiber foods.

You may feel slightly heavier or bloated, but this is a normal side effect. Glycogen is stored with water, so a temporary weight gain is expected and is a sign of a successful load.

It is best to spread your carbohydrate intake across the 1-3 days leading up to the race, rather than relying on one large meal. A high-carb breakfast 2-4 hours before the event is recommended to top off liver glycogen stores.