Complete Guide to Carbohydrate Loading for Endurance Athletes

Whether you're preparing for your first marathon, or  just looking to improve your performance in your next long-distance race, carbohydrates will play a key role in fuelling your race. One strategy that can help optimize performance during long-distance events is carbohydrate loading, commonly known as carb loading. By adjusting your carbohydrate intake and reducing exercise in the days leading up to a race, you can maximize your body's glycogen stores and ensure you have sufficient fuel to get you through the finish line.

What Is Carb Loading and Why Does It Matter?

Carbohydrates are your body's primary source of energy, and are especially important during exercise. When you consume carbohydrates, they are broken down into glucose, which can be used immediately for energy or stored in your muscles and liver as glycogen. During exercise, your body breaks down these glycogen stores to release glucose, providing your muscles with the fuel they need to keep you moving.

However, your body cannot store an unlimited amount of glycogen. During prolonged or high-intensity exercise, these stores gradually become depleted, making it increasingly difficult to maintain your pace, sustain performance and continue exercising. This is often referred to as hitting a wall, a common experience among marathon runners in particular. Carb loading helps delay glycogen depletion by increasing the amount of stored glycogen available to your body, allowing you to maintain energy levels for longer during endurance events.

How to Carb Load Before a Race

Carb loading involves increasing your carbohydrate intake while reducing your exercise volume in the days leading up to your event. For endurance events such as marathons or long-distance triathlons,  it is recommended to begin carb loading approximately 36-48 hours before race day.

During this period, endurance athletes should aim to consume approximately 10-12 g of carbohydrates per kilogram of body weight per day, alongside a significant reduction in physical activity. This combination allows your muscles to maximize their glycogen stores before the race.

It’s important to remember that carb loading does not mean simply eating more food or increasing your overall calorie intake. Instead, the goal is to adjust the proportions of your macronutrients by increasing carbohydrates while temporarily reducing fat and protein intake to make room for additional carbohydrates. Choosing foods that are lower in fat and fiber can also help reduce gastrointestinal discomfort, bloating and other digestive issues that may interfere with race-day performance.

What to Eat While Carb Loading

Choosing carbohydrate-rich, easily digestible foods can make it easier to meet your carbohydrate targets without feeling overly full or experiencing digestive discomfort. Lower-fibre carbohydrate sources are often preferred during this period, as they help provide energy while minimizing GI distress.

Some carbohydrate-rich foods to include in your diet during carb loading are:

Grains: White rice, white pasta, white bread, plain bagels, rice cakes, low-fibre cereals

Fruits: Bananas, applesauce, 100% fruit juice

Starchy vegetables: Peeled potatoes and sweet potatoes

Quick sources of carbohydrates: Plain crackers, honey, jam and other easily digestible carbohydrate-rich snacks

While increasing carbohydrate intake, it is equally important to be mindful of foods that may cause digestive discomfort. High-fibre foods, fried or greasy meals, excessive protein, cream-based sauces, spicy foods and gas-producing vegetables such as broccoli, cabbage and cauliflower should be avoided. It is also best to avoid unfamiliar foods in the days leading up to your race to reduce the risk of unexpected gastrointestinal issues.

Is Carb Loading Necessary for Every Race?

Carb loading is not necessary for every type of endurance event. For shorter distances, such as 5 km and 10 km races, your body's existing glycogen stores are generally sufficient to support performance, provided you are adequately fuelled beforehand.

For longer events, such as half marathons, some runners may benefit from carbohydrate loading before the race, depending on their pace, duration and individual nutrition needs. However, carb loading is particularly beneficial for endurance events longer than 90 minutes, as the prolonged duration of the event places greater demands on the body's glycogen stores.

Regardless of race distance, maintaining adequate carbohydrate intake as part of your regular training nutrition is important for supporting exercise performance, recovery and overall energy availability.

Fuel Your Next Race with a Plan

Carb loading can be a valuable strategy for endurance athletes, but individual carbohydrate requirements vary depending on body weight, training volume, exercise intensity, race duration and personal tolerance. Consuming too many carbohydrates without an appropriate plan can also lead to unnecessary digestive discomfort.

Working with a Registered Dietitian can help you determine your individual carbohydrate needs, plan meals and snacks, and develop a race-day nutrition strategy that supports your performance goals. A well-planned nutrition strategy can make a difference in how you feel, perform and recover on race day. 

Book in with Kate, Registered Dietitian, to receive a personalized carb loading plan for your next race!

References:

Mata F, Valenzuela PL, Gimenez J, Tur C, Ferreria D, Domínguez R, Sanchez-Oliver AJ, Martínez Sanz JM. Carbohydrate Availability and Physical Performance: Physiological Overview and Practical Recommendations. Nutrients. 2019; 11(5):1084. https://doi.org/10.3390/nu11051084 

Thomas, D. T., Erdman, K. A., & Burke, L. M. (2016). Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and athletic performance. Journal of the Academy of Nutrition and Dietetics, 116(3), 501–528. https://doi.org/10.1016/j.jand.2015.12.006