To Carb Load or Not to Carb Load, That is the Question!

Whether you’re new to racing or you’ve been in the game for years, you’ve likely heard that you should be “carb loading” the night before your race. But what does carb loading mean and is it really necessary and advantageous for you to carb load? Allow me to clear up some of your carb loading questions below!

Back up, what is a “carb”?

Carbs, or carbohydrates, are 1 of the 3 macronutrients (including protein and fat too) that get broken down by the body into sugar (mainly glucose) to be used as energy. Any excess carbs that don’t get used as energy get stored as glycogen in the liver and muscles. Some common sources of carbs are bread, oats, pasta, vegetables, fruits and other sources of sugar.

The reason carbs are brought up so much in running and other sports is because they are the primary source of fuel used by the body during high intensity (between 70% - 100% effort) activities. Research shows that the amount of muscle glycogen stores an athlete has can be the deciding factor in an athlete’s outcome (ex. Speed and endurance) of a race lasting longer than 60 minutes. Basically, the amount of glycogen an athlete has available plays a significant role in the athlete’s performance. 

So what is carb loading?

Carb loading is a term used to describe the act of increasing your carbohydrate intake the day or two leading up to your race. 

However, race nutrition and your performance is much more complex than just the day(s) leading up to your race. It is important that you are eating optimally throughout your training so that your body is a “well tuned machine” by the time your race rolls around. Just like you train your body through your workouts and physical activities, you must do the same with your nutrition leading up to your race event if you want to perform your best (and your mind too, but that is a post for another day).

Who should carb load?

According to the research on carb loading on varying distances of running races, only those running a marathon (42.2 km) or longer might benefit from actual carb loading. In this case, carb loading is defined as eating 10-12 grams per kg of body weight per day for 36 to 48 hours leading up to the race. Athletes running shorter races such as 10 km or even a half marathon may only need to increase carbs by 7-12 grams per kg of body weight per day (termed “glycogen normalization”) for a 24 hour period before the event to see benefits.

As you can see these are quite large ranges, emphasizing the need for personalization when it comes to running nutrition. And this doesn’t take into account the carb content of your pre-race meal on race day either.

It is important to note that individuals who have blood sugar abnormalities such as athletes with diabetes would also benefit from personalized recommendations on carbohydrate intake before and during a race.

Fiber beware

The literature also notes the importance of reducing fiber intake leading up to a race for athletes who experience digestive concerns during races. The reason I bring this up is because fiber is all the parts of plant based foods (carbohydrates) that the body cannot digest or absorb. So it matters what types of carbohydrates you are using to carb load, especially if you suffer from digestive symptoms during races. Some foods that contain high amounts of fiber include apples, beans and legumes, oats and avocados. For a full list of commonly consumed foods and their fiber content you can visit the following link: https://www.dietitians.ca/Downloads/Factsheets/Food-Sources-of-Soluble-Fibre.aspx

That being said, fiber is not your foe as an athlete! Fiber is important for bowel movement regularity and optimizing blood cholesterol levels. Reducing fiber intake prior to a race is only something you may want to pay attention to if you often suffer from digestive distress during activity. Another point to note is that you only want to reduce your fiber intake and not completely remove it from your diet. The literature recommends less than 10 grams of fiber per day for the 24-48 hours leading up to your event, however it varies person to person. This is another reason why personalized nutrition suggestions surrounding performance is so key.

The Bottom Line

Carb loading has been shown to be beneficial for athletes participating in the full marathon (42.2 km) distance race or activities lasting longer than 2.5 hours. Athletes can carb load up to 48 hours before the event by consuming 10-12 grams of carbs per kg of body weight per day. Athletes competing in shorter events may only need to increase carb intake by 7-12 grams per kg of body weight per day for 24 hours prior to their event to have maximal performance benefits.

If you already have a pre-race regime that works for you, I don’t recommend changing it. Always try out new nutrition approaches before and during training runs, not on race day. 

Calculating how many carbs you should be consuming during your training and leading up to your race day and what foods you should be getting your carbs from is complex. It requires a high level of personalized analysis by a healthcare provider knowledgeable in sports nutrition. If this is something you’re looking to improve, I’d love to help!

PS I offer free 15 minute consultations, click here to book: https://www.ndbri.com/schedule-appointment

References:

Prashant Nadkarni and Ruth S. Weinstock. Henry's Clinical Diagnosis and Management by Laboratory Methods, Chapter 16, 205-220.e2

https://www.dietitians.ca/Your-Health/Nutrition-A-Z/Fibre.aspx

https://www.dietitians.ca/Downloads/Factsheets/Food-Sources-of-Soluble-Fibre.aspx

Contemporary Nutrition Strategies to Optimize Performance in Distance Runners and Race Walkers. Burke, L., Jeukendrup, A., Jones, A., Mooses, M. International Journal of Sport Nutrition and Exercise Metabolism, 2019, 29, 117-129.

Essentials of Sport Nutrition and Supplements, J. Antonio, D. Kalman, J. Stout, M. Greenwood, D. Willoughby, G. Haff.