Carb Loading for Runners: A Guide to Maximising Your Energy Come Race Day

‘Carb loading’, less commonly known as ‘carbo loading’, is a proven fuelling strategy used by endurance athletes such as runners and cyclists to boost their energy levels and performance on race day. 

This is especially important for longer races such as marathons and ultramarathons.

The most simple way to summarise carb loading is eating more carbohydrates than usual in an attempt to increase the fuel stores available in your muscles. 

When done correctly, this should lead to improved performance and reduced feeling of fatigue.

However, carb loading before race day can be a confusing and intimidating prospect for many. Runners have to contend with different variables such as body types, genders, ages, metabolic rates, and even types of carbohydrates, all of which can make it hard to judge what to eat and when.

Luckily for you, we’ve done the research, and have broken down the core things you need to know here, making carb loading before a marathon or other event easier than ever!

First, let’s go a little more in depth on the basics:

What is Carb Loading?

As you may already know, carbohydrates are the body’s primary source of energy, making them arguably the most important food source for runners and endurance athletes.

Carbs that aren’t immediately used are stored as glycogen in muscular tissue and other organs such as the liver. The body is then able to access these stores during periods of endurance exercise such as a long run or bike ride.

That feeling you get when you’ve run for too long and suddenly struggle to maintain pace? That is scientifically known as glycogen depletion, but for the purposes of this post you can also call it carb depletion.

Carb loading is the strategy of increasing these glycogen stores above their normal levels by eating more carbs than normal for several days. It is unlikely to be beneficial for exercise shorter than 60 minutes, since this would rarely be enough for glycogen stores to run low. However, evidence strongly supports the benefits of carb loading for exercise over 60 minutes.

Where Did The Term ‘Carb Loading’ Come From?

The concept of carb loading was popularised by Ron Hill. one of the first UK ultra-runners. Ron prepared himself for the 1969 European Athletics Championships in Athens by using carb loading, something that later earned him pioneer status.

Ron had heard of the Saltin-Hermansson diet, which was based around glycogen depletion and was commonly used for cyclists at the time - but became the first known runner to use a similar strategy.

His success led to the popularisation of carb loading, and in the modern day it is commonly discussed and utilised by a wide range of athletes.

How Does Carb Loading Work?

The most common strategy for carb loading is eating higher levels of carbohydrates for 1-3 days before your race or event, although less exercise than usual is advisable for this time period too.

Studies support around 10g of carbs per 1kg of body weight per day, so a 90kg person may find 900g of carbs per day to be a good starting point.

It is important to note that this should also come alongside a reduction in fat and protein intake - so you’re increasing the ratio of carbs vs other nutrients, not increasing your total caloric intake overall.

What Are The Benefits of Carb Loading?

It’s important to reiterate that carb loading doesn’t provide benefits for all kinds of exercise, and is specifically of value for longer periods of exercise that are likely to decrease glycogen stores.

While this typically involves running, cycling and other endurance sports, it may also be helpful for sports that are played for over an hour like football or rugby.

As you might expect, when carb loading is done correctly, you can expect:

• higher levels of energy (study)

• reduced fatigue, or becoming fatigued later than usual (study)

• increased performance (study)

In other words, “hitting the wall” where you can no longer continue making a strong effort is what happens when your glycogen stores run low, so carb loading along with appropriate fuelling during your run are some of the most effective ways to avoid this and maintain your level of performance for longer.

Best Carb Loading Foods

Now that we’ve covered the why, you may be wondering how to carb load.

Anything high in carbs will help get you to your daily goal, so consider:

• Rice

• Pasta

• Noodles

• Potatoes

• Porridge

• Bread

• Bagels

• Pancakes

Fruits are also typically high in carbohydrates, however most are also high in fibre, which may cause a dash to the toilet mid race if too much is ingested.

A good high carb, low fibre fruit is the banana, iconic among runners for a reason!

A simple, easy way to begin eating carb loading meals is to add an extra serving of one of these foods to each meal - extra rice on the side of your dinner, or a bowl of porridge with breakfast, for example.

You may struggle to eat enough carbs to meet your exact goal on some days, but by simply trying, and by eating a lot more carbs than you usually would, you’re still storing up some extra glycogen.

Another easy way to get extra carbs between meals is a maple syrup energy gel. 

While these are primarily designed for fuelling and topping up your glycogen levels mid-run, they provide a significant 24g of carbs per gel, making them an easy way to top up your carbs between meals, taking advantage of liquid carbs for that extra boost if reaching your daily goal through food alone is a challenge.

Even better, you know they’ll go down well as they’re designed to be ingested during long races with no stomach discomfort.

When to Start Carb Loading

The sweet spot is typically 2–3 days before your event, especially for marathons or other long-distance runs. 

Start ramping up your carb intake to about 10g of carbs per kg of body weight each day, while scaling back on training to let your muscles stockpile the extra energy. 

For example, if you weigh 70kg, aim for 700g of carbs daily—think pasta, rice, and bananas, not donuts! Timing it right helps you avoid feeling bloated on race day, so plan your meals and keep it simple, ensuring you avoid any foods that are spicy or may upset your stomach like a hot curry.

So, carb loading is an important strategy, but ensure you plan this out in advance so you aren’t scouring the cupboard the day before your carb loading begins. Keep the foods you eat simple as well. Like with any nutrition strategy, never try anything new when it matters. Focus on high carb foods your body is used to, allowing you to reap the benefits on race day.