How does fuelling work? Fuel smarter and run the best race of your life!

How does fuelling work? Fuel smarter and run the best race of your life!

6-8 min. read 

Fuelling and nutrition, the misunderstood elements of endurance racing

When it comes to racing a marathon or a half-marathon, one of the most misunderstood subjects are the fuelling and nutrition requirements of these events. We all hear about the importance of consuming carbohydrates in the days leading up to the event, as well as taking in simple sugars through the form of gels, chews or bars - like XACT ENERGY fruit bars - during the race itself. But what is actually happening to all that fuel we put into our body? And what happens when we run out of fuel or glycogen (our body’s carbohydrate reserve) as we near the end of the race and hit the proverbial “Wall”?

Let’s break down this somewhat misunderstood portion of our sport and give you some basic science so that you can make sure you are fuelled and ready to run the best race of your life.

Just how many carbs do we need and how much can we actually store?

The average person can store around 2000 calories worth of carbohydrate in the form of glycogen. Most of this is stored in the muscles ready to be used, while some (about 400 calories) is in the liver and the bloodstream. To give you an idea of the weight of this reserve, 1 gram of carbohydrates = 4 calories.

Now, if a 150 pound person burns around 120 calories/mile and a marathon is 26.2 miles that individual would burn around 3150 calories in order to complete the marathon. If that runner was fully glycogen loaded they would need to make up around 1150 calories throughout the race.


that dreaded wall… and how to get through it! 

How would we accomplish that? Firstly, we would have something light for breakfast that tops us up and provides some energy to be burned early in the race, then during the event we would try to consume carbohydrate at a rate of 25 grams every 30-45 minutes through energy gels or XACT ENERGY fruit bars. Our body will also burn fat which contribute to our total need but at higher intensities like running a marathon, carbohydrates are a much more effective source of energy for our muscles. When we “hit the wall” our glycogen reserves are depleted and we start to get much slower.

So, by combining our glycogen reserves, body fat and breakfast with simple carbohydrates while we are running then we can keep the body fuelled properly to perform our best on race day!

What happens if we over consume carbohydrates  before the race?

Imagine your body like a car, and before the race we want our vehicle topped up with premium fuel. With that said, what happens when we try to fill a car’s gas tank but it’s already topped up? The excess gas spills out, this is what happens to our body when we go overboard the days before the race. Our body is very smart, when we are glycogen loaded, and we continue to take in carbohydrates exceeding our “storage limit” in liver and muscle tissue, our liver will break down the carbohydrates as glucose and release it into the bloodstream. When this occurs the body will release insulin from the pancreas and signal the fat cells to take in this excess glucose/energy and store if for a later time… in other words create fat. 

This is not ideal, as this “spills over” into fat cells and becomes non-essential mass that we will have to carry with us on race day. In the days before your race, eat at a moderate level with a high emphasis on carbohydrates in terms of percentage of overall caloric intake. This will ensure you get as much as you need without spilling over into fat production! This way the “fuel” you take on pre-race will propel you to your goals on race day!


Carbohydrate confusion

Hopefully this clears up some of the carbohydrate confusion out there. Stick with what has worked for you in your build up to the race. Eat foods that you know you tolerate well and leave you feeling energetic and satisfied. Be careful about trying something new. Trust your training and enjoy yourself!