Carbohydrate loading, or "carb loading," is a key endurance sports nutrition strategy. It involves increasing carbohydrate intake in the 2-3 days before an endurance event, such as a marathon or long-distance cycling race, to maximize muscle and liver glycogen stores. These glycogen reserves are essential for sustained energy and preventing the fatigue known as "hitting the wall".
The Science of Fueling Performance
During prolonged exercise, your body relies on carbohydrates for energy, stored as glycogen in muscles and the liver. While fat is also an energy source, glycogen is more efficiently converted to energy. For events over 90 minutes, normal glycogen stores are insufficient, leading to decreased performance.
Carb loading, through a high-carbohydrate diet (8-12g/kg body weight/day) and reduced training (tapering), increases glycogen to maximum capacity. This process, glycogen supercompensation, provides a larger fuel reserve, potentially enhancing endurance by up to 25% and performance by 2-3% in long events.
How to Execute a Successful Carb Load
- Start 2-3 days before the race: Gradual loading is more effective than a single large meal.
- Focus on easy-to-digest carbs: Choose low-fiber options like white pasta, rice, bread, and potatoes to avoid stomach issues.
- Reduce fiber and fat intake: Lowering these helps meet high carbohydrate goals without feeling too full.
- Prioritize familiar foods: Stick to foods you know agree with your system.
- Stay hydrated: Drinking fluids is important as glycogen stores water. Expect some temporary weight gain.
Complex vs. Simple Carbs for Loading
| Feature | Complex Carbohydrates (e.g., Pasta, Rice) | Simple Carbohydrates (e.g., Juice, White Bread) |
|---|---|---|
| Energy Release | Slow and sustained energy. | Quick energy burst. |
| Digestion Speed | Slower digestion. | Rapid digestion. |
| Fiber Content | Generally higher (reduce in final phase). | Lower (good for final 36-48 hours). |
| Best for Loading | Building core stores days before race. | Topping off stores or final meal. |
The Takeaway
Carb loading boosts endurance performance by maximizing energy reserves. A well-timed, low-fiber, high-carb diet combined with tapering prevents early fatigue. It's a strategic plan to ensure ample fuel for race day. Test your strategy in training.
Mottiv provides a useful guide on how to carb load for a marathon.
Conclusion
For events over 90 minutes, carb loading is a validated method to enhance performance by supersaturating glycogen stores. A gradual plan over 2-3 days using easily digestible carbs and tapering exercise maximizes energy capacity for race day.
