Do I Need To Fuel During A Half Marathon?

Half marathon races have become increasingly more popular over the last couple of decades, with more and more people signing up to take part in the 21 kilometer road-running event. 

One of the biggest areas of discussion around the half marathon distance is the question of fueling – both during the race and in the preparatory sessions leading up to the event. 

Is it a good idea to take on carbohydrate drinks and gels mid-race, or is this type of fuel best reserved for the full marathon distance? 

This guide will take an in-depth look at the best type of fueling to do in the build up to a half marathon event, as well as during the race itself. We’ll also look to answer some of the frequently asked questions. 

Energy demands

Before taking a look at fueling and nutrition, it’s important to understand some of the key energy demands of completing a half marathon. As is the case with all athletic events that last for longer than a few minutes, a large amount of the energy is delivered from oxygen-fueled aerobic metabolism in the body’s muscle cells. 

This is where fat and carbohydrates combine to supply the energy needed for muscle contraction. If the duration of your event is longer than 30 minutes, all energy is provided this way.

Given that even the world’s best half marathon runners take 59-60 minutes to complete the race, it’s fair to say that the event is fueled almost entirely through aerobic metabolism – irrespective of whether you’re an elite runner or a novice one. 

Another factor to take into account is the body’s carbohydrate storage. This is where the vast majority of elite runners have an advantage in the sense that muscle glycogen storage is only enough for around two hours of high-intensity activity.

Therefore, elite runners will usually have plenty left in the tank as they cross the line, whereas slower runners who’ll be racing for two hours or longer will use up their stores and become gradually slower. 

Pre-race fuelling 

Regardless of whether you’re an elite runner or just a casual runner, it’s essential to arrive at the start line with high levels of muscle glycogen. To ensure this is the case, you’ll need to consume a diet rich in carbohydrates in the 2-3 days leading up to the race, so plenty of bread, rice, pasta, potatoes, and so on. 

Of course, this also relies on you resting up during this period to conserve as much energy as possible. Furthermore, since glycogen is “fixed” into the body’s muscles with water, it’s important to take in plenty of fluids and cut down on alcohol. 

On the morning of the race, you should have an easily digested but carbohydrate-rich breakfast. This meal will ideally contain slow-releasing energy foods like oat-based cereals to reduce the likelihood of energy swings. 

Nutrition during the race

For elite runners and runners who are looking to finish the race in under 80 minutes, there’s no real need to take on carbohydrate drinks or gels to top up glycogen stores during the race. Just keep in mind that fluid is recommended in warmer conditions. 

If race duration is expected to be longer than 80 minutes, some use of carbohydrate drinks and gels is a good idea to top up glycogen stores. Roughly around 30 grams per hour is the recommended amount.

For race durations over a couple of hours, 60-75 grams of carbohydrate per hour will offset many of the severe effects of glycogen depletion. 

The key rule with carbohydrate supplementation is to test it in training first to see exactly how your body responds. For example, some runners are unable to tolerate gels, with gastric distress likely to contribute to a slower rather than faster finishing time. 

Nutrition during training 

Due to the fact that most runners’ training runs are shorter in duration than their expected race time, it’s not necessarily essential to use carbohydrate supplementation. However, as mentioned previously, they can help to keep muscles topped up, particularly for slower runners performing lengthy sessions. 

Despite the clear benefits of carbohydrate supplementation, there’s good reason not to consistently consume them during training. For example, when carbohydrates are easily available, the muscles of the body become considerably less efficient at burning fat. 

While your body’s capacity to burn fat isn’t vital for half marathon performance, it can help to schedule in some regular training sessions that are designed to enhance fat burning – especially if you’re looking to reduce body fat and increase your power-to-weight ratio. 

Lower levels of body fat will subsequently lead to reduced oxygen consumption and energy expenditure. It’s hardly surprising that pretty much all elite runners exhibit impressive power-to-weight ratios and low body fat levels. 

Frequently Asked Questions 

What should you not eat before a half marathon? 

To ensure you’re in a good physical condition for the race, it’s best to avoid foods that are rich in fiber as well fruits with skins such as pears and apples. Fiber-rich foods will increase your bowel movement before and during the race. Needless to say, this isn’t ideal.

Can you run a half marathon without any energy gels?

As mentioned previously, your body will usually start running low on stored glycogen around the 75-90 minute mark, so unless you’re a fast elite runner, it’s definitely beneficial to take an energy gel within the first hour to “top up” your stores. 

How long do energy gels take to kick in?

This can vary from runner to runner as every person processes carbohydrates at a different rate. Some runners may feel the effects of a gel in as little as three to four minutes, while others may have to wait for up to 15 minutes to reap the benefits. 

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