The Science of Carb Loading
Carbohydrate loading, or 'carb loading', is a nutritional strategy employed by endurance athletes to maximize the storage of glycogen in their muscles and liver. Glycogen is the body's primary fuel source for high-intensity, sustained exercise. While the body has limited glycogen stores, proper carb loading can top up these reserves, delaying fatigue and improving performance in events lasting longer than 90 minutes, such as marathons, triathlons, and ultra-endurance races.
Determining Your Ideal Carb Intake
The specific amount of carbohydrates required for effective carb loading varies based on an athlete's body weight and the event's duration. The most widely accepted recommendation is to consume 8–12 grams of carbohydrates per kilogram of body weight per day. For many athletes, this high volume can feel challenging, so practicing during training is essential to find what works for your body.
- For example: A 70kg (154lb) athlete aiming for the middle of this range (10g/kg) would need to consume 700 grams of carbohydrates per day for two to three days. This is a significant amount and requires careful meal planning, potentially including liquid carbohydrate sources like sports drinks or juices to reach the target without feeling overly full.
Timing Your Carb Load
The duration of your carb loading phase is as important as the quantity. The modern, and more common, approach involves increasing carb intake for 24–72 hours prior to the event, combined with a reduction in training volume (tapering). This contrasts with older methods that included a glycogen depletion phase, which is now considered unnecessary and potentially harmful. This shorter, more focused approach is effective and less demanding on the body.
- If your race is on a Sunday morning, you should begin your carb loading strategy on Friday morning or evening. This gives your body ample time to absorb and store the excess carbohydrates without a last-minute scramble.
Choosing the Right Foods
What you eat during carb loading is crucial for maximizing glycogen storage while minimizing gastrointestinal distress. It is recommended to choose easily digestible, lower-fiber carbohydrates, especially in the 24 hours immediately before the event. This helps prevent discomfort and bloating during the race.
Best Carb Loading Foods:
- White pasta and white rice: Easy to digest and high in starch.
- White bread and bagels: Simple and calorie-dense.
- Potatoes and sweet potatoes (without skin): Excellent sources of complex carbs.
- Oatmeal: A staple for many athletes, often consumed for breakfast.
- Bananas: Easy on the stomach and a good source of potassium.
- Sports drinks and juices: Efficient way to ingest carbohydrates without the bulk of solid food.
Foods to Limit or Avoid:
- High-fiber foods: Whole grains, beans, and certain vegetables can cause digestive issues.
- High-fat foods: Heavy sauces, fried foods, and rich desserts can slow digestion and cause sluggishness.
- Unfamiliar foods: Sticking to a tested and familiar diet is vital to prevent race-day surprises.
Sample Carb Loading Meal Plan
Here is a comparison table outlining a two-day carb loading strategy for a 70kg athlete aiming for 700g of carbs per day.
| Meal | Standard Day | Carb Loading Day | Notes |
|---|---|---|---|
| Breakfast | Oatmeal with berries (50g carbs), one egg | Large bowl of oatmeal with banana, dried fruit, honey, and a glass of orange juice (150g carbs) | Focus on easily digestible fruits and add liquid carbs. |
| Mid-Morning Snack | Small handful of almonds (5g carbs) | A large bagel with jam (80g carbs) | Simple carbs are easy to consume and digest. |
| Lunch | Chicken salad with mixed greens, and a side of quinoa (30g carbs) | Large portion of white rice with lean chicken breast (120g carbs), and a sports drink (40g carbs) | Reduce fiber and fat, and increase carb portion sizes. |
| Afternoon Snack | Apple and peanut butter (20g carbs) | An energy bar and a large banana (70g carbs) | Liquid or simple carb snacks work best. |
| Dinner | Grilled salmon with roasted vegetables (20g carbs) | Large plate of white pasta with low-fat tomato sauce and lean ground turkey (160g carbs) | Swap fattier proteins and heavy sauces for lighter options. |
| Evening Snack | Greek yogurt (10g carbs) | Two slices of white toast with honey and a sports drink (80g carbs) | A simple, easily digestible snack before bed. |
This table demonstrates how to shift your caloric intake from fat and protein towards a higher proportion of carbohydrates, rather than simply consuming more total calories. Athletes should reduce their training volume significantly during this period (tapering) to allow the glycogen to build up effectively.
Important Considerations and Best Practices
Hydration is Key
Carbohydrates are stored with water. For every gram of glycogen stored, your body holds approximately three grams of water. This means an increase in body weight is expected and is a sign of a successful carb load, not cause for alarm. Staying well-hydrated is critical during this period to facilitate this process. Drink plenty of water and electrolytes, which can also be delivered through sports drinks.
The Morning of the Event
Your race-day breakfast serves to top off your liver glycogen, which can be depleted overnight. Aim for 1-4 grams of carbohydrates per kilogram of body weight, consumed 1-4 hours before the race. This meal should also consist of familiar, easy-to-digest carbs. A bagel with jam or oatmeal with a banana are common, effective choices. If you have an early race, you might need to wake up earlier to eat and go back to bed.
Don't Overeat in One Sitting
One of the most common mistakes is trying to eat too much in one large meal, like a giant pasta dinner the night before. Instead, distribute your carbohydrate intake across smaller, frequent meals and snacks throughout the day. This is easier on your digestive system and more effectively maximizes glycogen stores.
Conclusion: Fueling Success on Race Day
Knowing how many carbs you should eat when carb loading is the key to unlocking peak performance for endurance events. By following the 8-12g per kg body weight guideline, starting 2-3 days prior to your race, and prioritizing easy-to-digest, low-fiber carbs, you can effectively maximize your body's glycogen stores. Remember to practice your fuelling strategy during long training runs to ensure you are confident and comfortable on race day. Combine this nutritional approach with a proper training taper and hydration plan to arrive at the start line feeling energized and ready to perform your best. By following these evidence-based strategies, you'll be well-prepared to outrun 'the wall' and achieve your race goals.
- For more detailed sports nutrition advice, consult the American College of Sports Medicine's guidelines: Nutrition and Athletic Performance
