What is a carb load for endurance?

November 11, 2025 •

2 min read

Studies have shown that carbohydrate loading can improve athletic performance and reduce fatigue by up to 2-3% for activities lasting over 90 minutes. A carb load for endurance is a strategic dietary and training technique where athletes maximize their body's energy reserves before a long-duration event.

Quick Summary

A carb load for endurance is a strategic nutritional plan to maximize muscle and liver glycogen stores before a long-duration event. This process, which typically involves increasing carbohydrate intake over several days, helps postpone fatigue and improves athletic performance. It is crucial to combine this with a tapering of training.

Key Points

Maximizes Glycogen: Carb loading is a strategy to maximize muscle and liver glycogen stores, which are the body's primary energy source for endurance activity.
For Events Over 90 Minutes: It is most beneficial for endurance events lasting longer than 90 minutes, like marathons and triathlons, and is not necessary for shorter events.
Combine with Tapering: Modern carb loading involves increasing carbohydrate intake alongside a reduction in training volume (tapering) in the 2-3 days before an event.
Choose Low-Fiber Carbs: Opt for easily digestible, lower-fiber carbs like white pasta, rice, and bagels, especially in the final 48 hours, to minimize the risk of GI distress.
Expect Temporary Weight Gain: A temporary increase in body weight (1-2kg) is normal due to the water stored with glycogen and is a sign of effective loading.
Practice During Training: It is crucial to practice your carb loading strategy during long training runs to test what foods and timing work best for your body.

The Science Behind Carb Loading

Carbohydrates serve as the primary fuel source for prolonged exercise, breaking down into glucose and stored as glycogen in muscles and the liver. These stores are essential for endurance activities lasting over 90 minutes; depletion can lead to significant fatigue or 'hitting the wall'. Carb loading is designed to increase these glycogen reserves, enabling athletes to maintain higher intensity for longer periods. Contemporary methods focus on increasing carbohydrate intake in the days leading up to an event, paired with reduced training volume, known as tapering.

How to Properly Execute a Carb Load for Endurance

Effective carb loading involves strategically increasing carbohydrate intake as a percentage of your diet, not just increasing overall food consumption. It is recommended to practice this strategy during training before a key event.

The Tapering and Loading Timeline

4-5 days pre-event: Begin significantly reducing training volume.
2-3 days pre-event: Increase carbohydrate intake to 7-12 grams per kilogram of body weight daily. Adjust fat and protein intake downwards to accommodate the higher carb intake and prevent digestive issues.
Morning of the event: Consume a low-fiber, carbohydrate-rich breakfast 2-4 hours before the start to replenish liver glycogen stores.

Smart Food Choices for Loading

Focus on easily digestible, carbohydrate-dense foods with lower fiber content. Good options include:

Pasta and Rice: White varieties are preferred for their lower fiber.
Potatoes: Both white and sweet potatoes work well.
Oats: A good breakfast choice.
Bagels and White Bread: Easily digestible bread products.
Bananas: Provide natural sugars and are easy on the stomach.
Juices and Sports Drinks: Convenient sources of liquid carbohydrates.

Pitfalls to Avoid

Overconsumption: Focus on macronutrient ratios, not just eating more food overall.
Trying New Foods: Stick to foods tested during training.
Neglecting Hydration: Glycogen storage requires water.
Excessive Fiber: Can cause digestive discomfort.

Comparison Table: Classic vs. Modern Carb Loading


Feature	Classic Carb Loading (Pre-2000s)	Modern Carb Loading (Today)
Depletion Phase	Required: High-intensity training and very low carb diet.	Not necessary: Focus on tapering training.
Loading Phase Duration	3-4 days.	Typically 24-48 hours.
Carb Intake (g/kg)	60-70% of total calories.	7-12 g/kg of body weight per day.
Side Effects	Increased fatigue and irritability.	Less stress, potential for temporary weight gain and bloating.
Effectiveness	Effective but stressful.	Effective and more practical.

Conclusion

Carb loading is a proven strategy for endurance athletes participating in events longer than 90 minutes. By maximizing glycogen stores through increased low-fiber carbohydrate intake in the days leading up to a race, combined with reduced training volume, athletes can delay fatigue and improve performance. It is important to practice this approach during training. Temporary weight gain is expected and indicates effective loading. For more information, consider resources like the Gatorade Sports Science Institute.

Frequently Asked Questions

You should start increasing your carbohydrate intake approximately 24-48 hours before your race, combining it with a taper in training to allow your body to store glycogen effectively.

If you don't carb load, your muscle glycogen stores may be insufficient for events over 90 minutes. This can lead to premature fatigue, reduced performance, and the experience of 'hitting the wall'.

Yes. Eating too many calories overall, or a very large meal at one time, can cause sluggishness, bloating, and digestive discomfort. The goal is to increase the percentage of carbs, not necessarily the overall food volume.

Ideal foods include easily digestible, lower-fiber sources like white rice, pasta, potatoes, bagels, and sports drinks. Avoid excessive fiber, fat, and protein which can cause digestive issues.

Carb loading is not necessary for shorter events like a 5K. A normal, balanced diet is sufficient, as your regular glycogen stores are typically adequate for exercise lasting less than 90 minutes.

No, a temporary weight gain of 1-2kg is normal. This is primarily water weight, as each gram of stored glycogen holds several grams of water, which is a sign of effective fueling.

Tapering, or reducing your training volume in the days before a race, is crucial for effective carb loading. It ensures that less glycogen is used, allowing the increased carbohydrate intake to be stored in the muscles.