A Guide to Carb Loading

by Ruby Wyles

So you’ve trained long and hard, your running shoes are practically glued to your feet, and the marathon start line beckons. But before you take off, there’s one crucial step many runners and sports dietitians alike swear by: carb loading.

What is Carb Loading?

Carb loading is a dietary strategy designed to maximize your body’s stores of glucose, known as glycogen, the primary fuel source for muscles during exercise. By strategically increasing your carbohydrate intake in the days leading up to your race, you aim to have a “full tank” of energy ready to power you through those arduous miles.

Why Carb Load for a Marathon?

During a marathon, or any race over 2 hours, your body will deplete its glycogen stores. As your body burns through its fuel source, you might experience the dreaded “hitting the wall” – a sudden drop in energy levels that can derail your entire race. Carb loading helps prevent this by ensuring your body has enough readily available glycogen to sustain a strong pace.

How to Carb Load Like a Champion

Carb loading isn’t about stuffing yourself with donuts and pasta the night before. It’s a calculated approach with specific timing and food choices. Here’s a breakdown:

  • Timing: Aim to start carb loading 3-6 days before your race. This window allows your body time to convert the extra carbs into glycogen. It also allows for a more conservative increase in carbohydrate intake as opposed to a dramatic ramp up the day or two before, risking negative GI symptoms and feeling uncomfortable.
  • Quantity: The recommended daily intake is 7-12 grams of carbs per kilogram of body weight. So, a 70kg (155lbs) runner would target 490-840 grams of carbs each day. However, instead of simply adding in extra carbs on top of your daily diet, think about rebalancing your normal meals: reduce the amount of proteins, fats, and high fiber foods like vegetables, and replace them with carbohydrates.
  • Quality: Not all carbs are created equal. Focus on easily digestible, low-fiber options like white rice, potatoes, bananas, bagels, and cereals. These provide a steady stream of energy without causing stomach upset.
  • Don’t Ditch Other Nutrients: While carbs are king, don’t completely eliminate protein and healthy fats. Include lean protein sources like chicken and fish, and healthy fats from nuts and avocados to support muscle recovery and overall health.
  • Practice Makes Perfect: Don’t experiment with new foods during carb loading. Stick to meals and snacks you’re familiar with to minimize digestive issues on race day.
Blueberry muffins make a great high carb snack! PC: Ruby Wyles

Example meals and snacks:

  • Bagel with avocado and eggs/ banana and peanut butter
  • Baked potato with cheese
  • Pretzels
  • Sports drink or fruit juice
  • Low fiber cereal with milk
  • Gummies and other candies
  • Spaghetti/ other pasta
  • Chicken or fish with white rice
  • Oatmeal with mixed berries
  • Yogurt with berries and nuts
  • Muffins or waffles 

Remember: Carb loading is just one piece of the nutrition puzzle. Proper hydration and a well-practiced race day fueling plan are equally important for marathon success.

By following these tips and consulting a registered dietitian for personalized advice, you can ensure your body is optimally fueled to conquer your endurance goals!

Ruby is a runner, triathlete, and passionate coach, who is most fulfilled by helping athletes overcome limiting beliefs with joy. She is also a proud science nerd, and advocate for athletes’ mental and physical health.