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  • Melissa Paauwe

Why do we carb load?

All runners know that they should carb load before a long-distance race. But I’m willing to bet that many, like me until recently, didn’t know the scientific reasons behind it. Here’s what I’ve learned:

Our bodies store glycogen in our muscles and liver which is converted to glucose and used as fuel when we exercise. Glycogen stores can take up to 20 hours to fully replenish once used up. Even if topped off fully they are not likely enough, for the typical runner, to complete a marathon without hitting the dreaded wall if additional carbs are not ingested during the race.

Carb loading should be done in conjunction with a taper to see the most benefits. The simple reason for this is exercise at high intensity and long duration will deplete our glycogen stores. The taper period allows our glycogen stores to slowly build while not losing fitness with shorter duration and shorter intensity bursts. Carb loading is not one meal. It consists of a period of time, as many as 3-7 days pre-race, to start consuming enough carbs to top off glycogen stores. One could not eat enough carbs to do this one day prior to race day to ensure glycogen levels are topped off. Therefore, carb loading the night before, although still recommended, would not be enough to ensure topped off glycogen levels. One thing worth noting is that a slight weight gain can happen during this carb loading phase. Is it there to stay? Unlikely! One marathon alone burns thousands of calories and the weight gain is attributable to the increase water stored in muscles. Carbohydrates are made up of hydrogen (water), oxygen, and carbon. The increase of carbohydrates stored in your muscles mean increased water weight which will surely be sweated out and used up during the race! So, eat that plate of pasta guilt free and pat yourself on the back for the baked potato the night before that. Does mac and cheese count? Why not (as long as cheese doesn’t cause you gastrointestinal issues). I’m pretty sure poutine has a high level of carbs too. Your body will thank you when you can say “what wall?” that next race you do!

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