Nutrition Diet: What is the optimal carb loading intake?

October 15, 2025 •

4 min read

For endurance events lasting over 90 minutes, your body's glycogen stores are often depleted, leading to fatigue. This makes understanding what is the optimal carb loading intake a critical nutritional strategy for improving performance and pushing through the finish line.

Quick Summary

Carb loading is a strategy for endurance athletes to maximize muscle glycogen stores before a race. Optimal intake typically falls between 8-12g per kg of body weight over 48-72 hours, using low-fiber, high-carb foods to delay fatigue and enhance performance.

Key Points

Target Intake: Aim for 8-12 grams of carbohydrates per kilogram of body weight per day for long endurance events.
Timing is Key: Begin carb loading 48 to 72 hours before an endurance event lasting over 90 minutes.
Choose Low-Fiber Carbs: Stick to easily digestible options like white pasta, rice, and bagels to avoid gastrointestinal issues.
Stay Hydrated: Drink plenty of water, as glycogen stores require water. A temporary weight gain is normal.
Practice Your Plan: Never try a new carb loading strategy on race day. Practice during long training runs to test your tolerance.
Top Off Before the Race: Eat a high-carb meal 1-4 hours before the event to replenish liver glycogen stores.

Maximizing Your Fuel Tank: Understanding Carb Loading

Carbohydrate loading is a well-researched nutritional strategy used by endurance athletes to maximize the amount of glycogen stored in the muscles and liver. Glycogen is the body's primary fuel source for high-intensity, prolonged exercise. By filling these stores to their maximum capacity before an event, athletes can delay fatigue and sustain a higher performance level for longer durations. While the concept is simple, the execution requires a strategic approach to timing, quantity, and food selection.

Determining Your Optimal Intake

The optimal amount of carbohydrates to consume during a loading phase depends on several factors, including your body weight and the duration of your event. For most endurance athletes competing in events lasting more than 90 minutes, the recommendation is to consume between 8 and 12 grams of carbohydrates per kilogram of body weight per day. For a 70 kg athlete, this translates to 560 to 840 grams of carbohydrates daily. This is a significant amount and can feel like a lot of food, which is why proper planning is essential.

The Timing of Your Carb Load

Modern carb loading protocols have moved away from the more extreme 'depletion and loading' methods of the past. The current standard involves a more straightforward approach of increasing carbohydrate intake for a specific period while tapering training volume.

48 to 72 Hours Before the Event: This is the ideal timeframe to begin the loading phase. By increasing carbohydrate intake and reducing your training, your muscles become primed to store glycogen efficiently.
Race Morning: A pre-race meal consumed 1-4 hours before the start is vital for topping off your liver glycogen stores, which can be depleted overnight. Recommendations range from 1 to 4 grams of carbohydrate per kilogram of body weight.

Choosing the Right Carbohydrate Sources

During the carb loading phase, the focus should be on easily digestible, low-fiber carbohydrate sources to avoid gastrointestinal distress on race day. Bulky, high-fiber foods can fill you up too quickly, making it difficult to meet your high carb goals.

Recommended High-Carb Foods:

Grains: White bread, bagels, pasta, white rice, low-fiber cereals like cornflakes or rice krispies.
Starches: Potatoes, sweet potatoes, pretzels.
Fruits: Lower-fiber fruits like bananas, melons, and grapes. Jams, honey, and maple syrup are also excellent.
Beverages: Fruit juice, sports drinks, and sweetened yogurt.
Supplements: Energy gels and carbohydrate drink mixes can help hit high carb targets without excessive bulk.

Foods to Limit:

High-Fiber Foods: Whole grains, legumes, and most raw vegetables. While healthy, their high fiber content can cause bloating.
High-Fat and High-Protein Foods: These slow digestion and can interfere with maximizing your carb intake.

The Importance of Hydration and Other Considerations

During carb loading, it is crucial to maintain adequate hydration. Every gram of stored glycogen is bound to approximately 3 grams of water. This means consuming sufficient fluids is essential for proper glycogen storage and performance. Athletes may notice a temporary weight gain of 1-2 kg, which is primarily water weight associated with the increased glycogen and is a positive sign that loading is on track.

It is highly recommended to practice your carb loading strategy before a key event. This allows you to test your tolerance for certain foods and quantities, identify any potential digestive issues, and get accustomed to how your body feels with maxed-out glycogen stores. For those with medical conditions like diabetes, it is essential to consult a physician or registered dietitian before attempting a high-carbohydrate regimen.

Carb Loading: A Comparison for Different Event Durations


Feature	Short Duration Events (<90 min)	Long Duration Events (>90 min)
Necessity	Not necessary; normal glycogen stores are sufficient.	Highly recommended to boost endurance and delay fatigue.
Loading Phase	A high-carb meal 3-4 hours before the event is usually enough.	48-72 hours of increased carbohydrate intake is recommended.
Intake Target (per day)	No specific target, just ensure adequate daily carbs.	Aim for 8-12 grams of carbohydrate per kg of body weight.
Training Taper	Less critical for shorter events.	Essential to reduce volume and intensity to allow for proper glycogen storage.
Food Choices	Stick to familiar, well-tolerated foods.	Focus on low-fiber, easily digestible carbs to maximize intake without discomfort.

Conclusion

What is the optimal carb loading intake? It is a targeted, event-specific strategy that involves consuming 8-12 grams of carbohydrate per kilogram of body weight over 48 to 72 hours, alongside reduced training. By prioritizing low-fiber, easily digestible carb sources and maintaining excellent hydration, endurance athletes can maximize their muscle glycogen stores and significantly improve their performance. This strategy is most effective for events lasting longer than 90 minutes, and practicing your plan during training is key to success on race day. For a detailed look at sports nutrition principles, consult the comprehensive guidelines provided by experts such as Sports Dietitians Australia.

Note: For individuals with health concerns or dietary restrictions, consulting a registered dietitian is always recommended before making significant dietary changes.

Frequently Asked Questions

No, carb loading is generally only beneficial for endurance events longer than 90 minutes, such as marathons or long-distance cycling. Your normal glycogen stores should be sufficient for a shorter race.

Focus on easily digestible, low-fiber sources like white rice, pasta, bagels, potatoes, and sports drinks. Avoid excessive fiber, fat, and protein in the final 48 hours to minimize stomach discomfort.

Yes, a temporary weight gain of 1-2 kg is normal and expected. This is due to the extra water that is stored along with the glycogen in your muscles and is a good sign that your loading is on track.

For endurance events, you should begin your carb loading phase 48 to 72 hours before the competition. This should be combined with a reduction in your training volume.

For events over 90 minutes, the recommended daily intake is 8 to 12 grams of carbohydrates per kilogram of body weight. The specific amount within this range depends on the event's duration and your individual tolerance.

Consuming too much fiber during carb loading can cause gastrointestinal distress, including bloating, gas, or diarrhea, which can negatively impact performance on race day.

While it's important not to eliminate them entirely, you should reduce your intake of protein and fat. They take longer to digest and can make it difficult to consume the large quantity of carbohydrates required for effective loading.