What is a long-distance runners carb load and How to Master It

November 21, 2025 •

2 min read

Studies show that proper pre-race fueling can improve endurance performance by up to 3% in events over 90 minutes. Understanding what is a long-distance runners carb load is a vital nutritional strategy for maximizing energy reserves and ensuring you finish strong.

Quick Summary

Carb loading is a nutritional strategy for endurance runners that increases muscle and liver glycogen stores before a major event. This boosts the body's primary energy reserves to delay fatigue and improve performance on race day.

Key Points

Modern Method: Increase carbohydrate intake while tapering training 36-48 hours pre-race.
Target Intake: Aim for 10-12 grams of carbohydrates per kilogram of body weight daily.
Focus on Low-Fiber Carbs: Reduce fiber 1-2 days before the race using simpler carbs to avoid stomach issues.
Timing is Key: Spread carb intake across smaller, frequent meals.
Stay Hydrated: Drink plenty of fluids as glycogen stores water.

The Science of Carbohydrate Loading

For endurance athletes, carbohydrates are the body's primary energy source. Glucose from consumed carbs is stored as glycogen in muscles and the liver, fueling runs, especially intense, long efforts. Natural glycogen stores power about 90 minutes of exercise before depletion, leading to the 'wall'. Carb loading increases glycogen beyond normal capacity to delay fatigue in races over 90 minutes. This involves boosting carb intake and reducing training (tapering).

The Modern Carb Loading Strategy

Older carb loading included a stressful depletion phase. The modern approach skips depletion, focusing on increased carbs and tapering in the days before a race. Tapering allows muscles to efficiently store excess carbs as glycogen.

How to Execute a Successful Carb Load

Implement these steps for effective carb loading:

Timing: Start 36-48 hours pre-race; earlier has no extra benefit.
Target: Aim for 10-12 grams of carbs per kg of body weight daily. A 70kg runner needs 700-840g daily.
Reduce Fiber: Eat low-fiber carbs like white bread and rice in the final 24-48 hours to prevent GI issues.
Focus on Carbs: Prioritize carbs over total calories by slightly reducing fat and protein.
Stay Hydrated: Glycogen stores water; increase fluid intake for storage and hydration.
Don't Overeat at Once: Consume carbs via smaller, frequent meals and snacks.

Comparison of Carbohydrate Food Sources


Type	Examples	Best For	Considerations
Complex Carbs	Pasta, rice, potatoes, oats, bread, quinoa	Sustained energy during training and early loading	Limit close to race day due to fiber
Simple Carbs	Energy gels, sports drinks, fruit juice, bananas, energy bars	Quickly topping up glycogen; mid-race fuel	Can cause blood sugar spikes

Common Mistakes and How to Avoid Them

A frequent mistake is a large meal the night before, which doesn't allow time for glycogen storage and can cause bloating. Not reducing fiber is another pitfall, leading to GI distress. Neglecting hydration hinders carb storage. Practice your strategy during training to find what suits you. For more fueling advice, see A runner's guide to carb loading for a marathon.

Conclusion

A successful carb load is a strategic pre-race plan to maximize muscle fuel. The modern method involves increasing easily digestible carbs while tapering, ensuring optimal energy for race day performance and avoiding the wall.

Frequently Asked Questions

For most events over 90 minutes, start carb loading 36 to 48 hours before the race.

Choose low-fiber, high-carb foods like white rice, pasta, white bread, bagels, potatoes, and sports drinks that you've practiced with.

No, it's generally not needed for races under 90 minutes; a normal diet suffices.

A temporary gain of 2-4 lbs from water stored with glycogen is normal and positive.

Yes, but in reduced amounts, prioritizing carbs over total calorie increase.

Have a carb-rich, low-fiber, low-fat meal 2-4 hours pre-race, like oatmeal or a bagel with jam.

Maintain high carb intake across the loading period with smaller, frequent meals and snacks.