The Truth About Carb-Loading For Half Marathons

by | Apr 30, 2021 | Technical Articles

What should you eat to fuel up for the Windsor half-marathon?

Carb-loading is one of the prevailing theories linked with endurance running. But is the idea of fuelling up on a carb-heavy meal before a half marathon fact, or fiction? We’ve looked into the concept of carb-loading so you can prepare for the Windsor Half Marathon 2021 the best way possible.


What Is Carb Loading?

Carb loading (carbohydrate loading) refers to the idea of loading up on carbohydrate before a long run. It’s based on the knowledge that our bodies store carbohydrate as glycogen in the muscles and liver. This stored energy is then used to fuel long bouts of energy – like running a half marathon! But the idea of carb loading can often be misconstrued, with people overeating on carb-heavy foods without understanding how much carbohydrate the body can store – or what kind of carbohydrate to eat.


Carbohydrates & Endurance Running

Our bodies run on energy, which comes from calories (a unit of energy). This should mean that any calories will fuel the body up for running. However the truth is a little different. Carbohydrate – stored as glycogen – is the body’s preferred form of fuel, especially for this kind of running. That’s why energy drinks, gels, and traditional running fuel is high in carbohydrate and very low in fat.


The Science Of Carb Loading?

When we eat and digest carbohydrate, it gets stored in our muscles and liver (as glycogen). During endurance running, our body needs energy. Those glycogen stores are the most easily accessible forms of energy for the body to tap into. The stored glycogen gets converted to glucose again, and this is used to fuel our running.

The average human body can store 350g-500g glycogen in muscles. Now this is where things get interesting – that stored glycogen is only enough to fuel about 90 minutes of endurance exercise, like running. So unless you want to hit the wall during your race, you’ll need to top up with more carbs during the race.


Hitting The Wall?

How is carbohydrate-loading linked to hitting the wall during running? The body can also use fat as a fuel to generate energy, but it’s hard work (and it really doesn’t like to do it!) It’s a more complex process, takes longer, and is more metabolically taxing than using glycogen from carbs. If you run out of carbohydrate-based energy and switch to using fat for fuel, you’ll feel it! This is what’s known as hitting the wall in endurance running. and slower.


What To Eat Before A Half Marathon

We already know that our muscles can only hold 500g max of glycogen from carbs. So is it worth really “loading” with carbohydrate?

> You can’t fill your muscles with glycogen from just one meal

> If you overeat carbs the night before the race, your body won’t have enough time to digest it all

> You can “carb load” but it takes longer than just one meal

Start increasing your carbohydrate sources 3 days before the race. You’ll be tapering on these days anyway, so the reduction in mileage and increase in carbs will naturally boost your glycogen stores in muscle tissue.

Don’t overdo it. Keep your total calorie intake normal, but increase the % of carbs by slightly bringing down fats, and filling this space with carbs. Aim for 70% of total calories from carbohydrates over these 3 days. Use low-fat, unprocessed foods (not junk foods!) like rice, pasta, potatoes, fruit, oats, rice cakes, and light bread products like pittas and wraps. Scale back on fibrous carbs (from vegetables) the night before the race to reduce any bloating.

The night before the race, eat a normal sized meal that is heavy on the carbs and low in fats. Don’t eat too late – give your body enough time to digest. It’s OK to wake up a bit hungry on race day – you’ll be having breakfast anyway before the run.


Windsor Half Marathon Sunday September 26th 2021 Click here to enter now