Understanding the Role of Carbohydrates for a 50k
For an ultra-marathon, your body primarily relies on two energy sources: stored fat and stored carbohydrates, known as glycogen. While your fat stores are vast, your glycogen stores are limited and can be depleted within a couple of hours of intense running. Carbohydrates are the faster-burning, more efficient fuel source, making them essential for high performance over long distances. The central goal of your fueling plan is to keep your glycogen stores topped up for as long as possible to sustain your energy levels and delay fatigue.
The Science of Carb Loading
Carb loading is the process of maximizing your muscle and liver glycogen stores in the days leading up to an endurance event. This practice can significantly improve performance for events lasting longer than 90 minutes. It's no longer about a severe, old-school depletion phase, but a more modern, athlete-friendly approach.
- Start 2-3 Days Before: Begin increasing your carbohydrate intake and decreasing your training volume around 48-72 hours before the race.
- Increase Carb Ratio: Aim for a daily intake of 7-10 grams of carbohydrates per kilogram of body weight. For a 70kg runner, this means consuming 490-700 grams of carbs daily.
- Choose Easily Digestible Foods: Focus on low-fiber, compact carb sources to avoid gastrointestinal (GI) distress. Examples include white bread, rice, pasta, and potatoes. Liquid carbs from sports drinks can also be very helpful.
- Reduce Fat and Protein: While not eliminated, the proportion of fat and protein in your diet should be reduced during the carb loading period to prioritize glycogen storage.
Fueling Strategy During the 50k
During the race itself, consistent and early fueling is paramount. Do not wait until you feel hungry or low on energy, as it is often too late to recover effectively.
- Start Early: Begin consuming fuel within the first 30-45 minutes of the race.
- Consistent Intake: Most ultra-runners should aim for a steady intake of 60-90 grams of carbohydrates per hour. Experienced athletes who have trained their gut may be able to tolerate upwards of 100g/hour.
- Use Multiple Carb Sources: A blend of glucose and fructose sources is most effective for maximizing carbohydrate absorption and minimizing gastric upset. Many sports nutrition products are formulated with this 2:1 ratio. For longer races, a mix of simple and complex carbs from various sources is recommended to prevent palate fatigue and potential GI issues.
Comparison of Fuel Sources
| Fuel Source | Carbohydrates per Serving | Digestibility | Best For | Potential Drawbacks |
|---|---|---|---|---|
| Energy Gels | 20-40g | Fast | Quick energy boosts | Can cause stomach upset if not taken with water |
| Energy Chews/Blocks | 20-30g | Fast to Moderate | Easy to portion out | Can be chewy and require more effort to consume while running |
| Liquid Calories (Sports Drink) | 30-60g+ per 500ml | Very Fast | Hydration and fuel combined | Can lead to flavor fatigue and stomach issues with high concentration |
| Real Food (e.g., Potatoes) | Varies | Slower | Psychological boost, savory cravings | Can be heavier to digest, need to be prepared and carried |
| Energy Bars | 25-50g+ | Moderate | Sustained energy | Can feel heavy in the stomach, hard to chew while running fast |
Gut Training
Your ability to absorb carbohydrates during a race is not limitless and can be improved through training. Gut training involves intentionally consuming race-day nutrition during your long training runs to acclimate your digestive system.
- Practice Consistently: Test out your planned race-day nutrition on your long runs. Don't wait until race day to experiment with new gels or foods.
- Mimic Race Conditions: Practice fueling at race pace and in similar environmental conditions (e.g., heat) to see how your stomach reacts.
- Start Small: If you're new to high carb intake, start with 30-60g/hour and gradually increase over time.
Race Day Execution and Recovery
On race day, trust your plan. The morning of the race, have a light, carb-rich breakfast 2-3 hours before the start. During the race, use reminders to stay on schedule. After you cross the finish line, your recovery fueling is critical. Aim for a 3:1 or 4:1 carbohydrate-to-protein ratio within 30-60 minutes to replenish glycogen stores and aid muscle repair. Pizza, chocolate milk, or a recovery shake are popular choices.
Conclusion
Mastering your carbohydrate intake is fundamental to success in a 50k ultra-marathon. By implementing a strategic carb-loading phase, practicing consistent fueling during long training runs, and executing a well-rehearsed plan on race day, you can optimize your energy levels and performance. Remember, the exact quantity of carbs varies per individual, so listen to your body and train your gut to discover what works best for you.
