The Science Behind Carb Loading
For endurance events like a marathon, your body primarily uses stored carbohydrates, called glycogen, for fuel. These stores in your muscles and liver provide the necessary energy for sustained activity. In events exceeding 90 minutes, these glycogen stores can deplete, leading to extreme fatigue, often referred to as 'hitting the wall'. Carb loading aims to significantly increase these glycogen reserves, providing a larger fuel supply from the start of the race. This can help maintain a higher intensity for a longer period, improving overall performance and delaying the onset of fatigue. Research suggests that a high-carbohydrate diet can enhance performance by up to 3% in events lasting over two hours.
The Modern Carb Loading Method
Modern sports nutrition recommends a carb loading approach that avoids the previous method's depletion phase. The current strategy involves increasing carbohydrate intake for 2-3 days before your race while simultaneously reducing training volume (tapering). This allows your body to store the extra glycogen efficiently. A common guideline is to consume 7-12 grams of carbohydrates per kilogram of body weight daily during this period. For example, a 70kg runner would aim for 490-840 grams of carbs per day. To accommodate this increase without overeating, it's advised to decrease your intake of fats and proteins.
What to Eat: The Right Food Choices
During carb loading, selecting easily digestible, low-fiber carbohydrates is crucial to prevent stomach issues on race day. Focus on familiar, well-tolerated foods, prioritizing refined grains over whole grains.
Examples of high-carb, low-fiber foods:
- White pasta with low-fat sauce
- White rice
- Bagels and white bread with jam or honey
- Bananas and low-fiber fruits (like applesauce)
- Low-fiber cereals (cornflakes, rice krispies)
- Peeled, boiled potatoes or sweet potatoes
- Sports drinks and fruit juices
- Energy gels and chews (practice during training)
Foods to limit or avoid:
- High-fiber vegetables (broccoli, beans)
- Whole-wheat products
- High-fat foods (creamy sauces, fried items)
- Excessive protein
- New or untested foods
Comparison of Carb Loading Foods
| Food Type | Pros | Cons |
|---|---|---|
| White Pasta/Rice | High in carbs, low fiber, easy to digest. | Can be filling, requires portion control. |
| Bagels/White Bread | Easy to eat, portable, quick energy. | Can be very filling. |
| Bananas/Fruit Juice | Quick-digesting, convenient, aids hydration. | Can be high in sugar, some fruits have higher fiber. |
| Sports Drinks/Gels | Concentrated carbs, portable, electrolytes. | Can cause stomach issues if not practiced, high in simple sugars. |
| High-Fat Foods | N/A (limit during carb loading). | Slows digestion, can cause upset, not carb-dense. |
| High-Fiber Foods | Generally healthy, but not for carb loading. | Can cause bloating, digestive problems, reduce carb absorption. |
Common Carb Loading Mistakes to Avoid
To ensure a successful marathon fueling strategy, avoid these common errors:
- Overeating: Focus on increasing the proportion of carbs, not just eating more food overall.
- Starting Too Late: Carb loading requires 2-3 days, not just the night before, for effective glycogen storage.
- Trying New Foods: Stick to familiar foods during your taper to avoid unexpected digestive issues.
- Neglecting Hydration: Adequate water intake is essential for storing glycogen.
- Skipping Practice: Practice your carb loading during long training runs to understand how your body reacts.
Conclusion
For marathon runners and participants in events over 90 minutes, proper carb loading is a scientifically supported strategy to improve performance. By increasing your intake of easy-to-digest, low-fiber carbohydrates in the 2-3 days leading up to your race, you can maximize muscle glycogen stores and help prevent hitting the wall. Remember to plan, practice during training, stay hydrated, and adjust your overall diet by lowering fat and protein to make room for the extra carbs. This preparation, along with your training, will help you perform your best. For more detailed guidance on endurance fueling, consult resources from sports nutrition organizations like the American College of Sports Medicine.
The Morning of the Race
On race morning, eat a familiar, high-carb breakfast 3-4 hours before the start to allow for digestion and replenish liver glycogen.
