Carbohydrate loading – how, when and why?

Carbohydrate loading before a competition is something athletes have been doing for many years, particularly in endurance sports such as running, cycling and cross-country skiing. But how important is it really, how much carbohydrate do you need to consume, and do you really have to eat pasta for three days before a race? 

Grafen visar hur muskelglykogenet återhämtade sig under sex dagar efter ett glykogentömmande träningspass.

The body stores carbohydrates in the form of glycogen, primarily in the muscles and liver. An average person has approximately 400–600 g of stored glycogen, but the amount varies depending on factors such as muscle mass, training status and how much carbohydrate you consume.(1)

These stores are an important energy source during training and competition, especially at higher intensities. The harder you work, the greater the proportion of energy that comes from carbohydrates.

The problem is that these stores are limited. During longer and more strenuous activities, glycogen levels can drop so much that it becomes difficult to maintain the same intensity. This is one of the reasons we can experience the famous “wall” during a marathon, for example.(1)

By eating extra carbohydrates before a competition, you can increase the amount of glycogen stored in your muscles. This is known as glycogen supercompensation and simply means that you start with greater energy reserves than normal.(1)

In other words, more fuel in the tank from the start!

Research shows that a carbohydrate intake of approximately 8–12 g per kilogram of body weight per day can be effective for maximising glycogen stores before a longer endurance event.(1, 2) This calculation applies as long as you are at a healthy weight. If your BMI indicates overweight or obesity, you may benefit from reducing your intake slightly and aiming for the lower end of the range.

But to keep things simple, let’s use 10 g/kg of body weight as a guideline. If you weigh, for example, 80 kg, your target is therefore 800 g of carbohydrates per day. That’s quite a lot of food!

To put this amount into perspective, 800 g of carbohydrates is approximately equivalent to:

• 1 kg uncooked pasta
• 1.3–1.5 kg oats
• 35 bananas

However, we do not recommend forcing down 35 bananas or spooning down 35 servings of porridge; instead, you should get your carbohydrates from a varied, balanced diet! You get carbohydrates from a wide range of foods throughout the day, and it is the total intake that counts. Pasta, rice, bread, potatoes, fruit, juice and other carbohydrate-rich foods can help you reach your target.

In other words, what matters most is not exactly which carbohydrates you eat, but that you consume enough of them. However, the type of carbohydrate largely determines how easily you can reach an intake of 800 g per day. It is very difficult to consume that amount from boiled potatoes alone, even if you love them. That is why it is generally recommended to include some easily digestible carbohydrate sources during carbohydrate loading.

The recommendation used to be to first deplete your glycogen stores through hard training and a low-carbohydrate intake, and then consume a very large amount of carbohydrate over several days.

You no longer need to do that!

Research shows that you can achieve very high glycogen levels simply by reducing your training volume and increasing your carbohydrate intake before competition.(1, 3)

Studies have also shown that as little as 24 hours of a sufficiently high carbohydrate intake may be enough to achieve a substantial increase in muscle glycogen, particularly in well-trained individuals with a good capacity for rapid glycogen storage.(3)

However, this needs some nuance. The body of research shows that 36–48 hours of a high carbohydrate intake is a more reliable general recommendation if the goal is to maximise glycogen stores.(1)

For most people, this means focusing on consuming extra carbohydrate during the final 1–2 days before competition. You generally do not need to continue for longer than that.

And remember to reduce your training at the same time. It is considerably easier to replenish your energy stores if you do not use up large amounts of glycogen during carbohydrate loading.(1)

You don’t need to follow a full carbohydrate loading protocol before every competition.

For shorter activities, such as running 10 km in under 60 min, your muscles will normally contain enough glycogen to complete the event on a regular diet, which typically provides 5–6 g of carbohydrate per kg of body weight on a healthy mixed diet.

Carbohydrate loading is usually most beneficial for longer activities where glycogen availability can become a limiting factor. A half marathon or marathon is a good example. Activities lasting around 90 minutes to 2–3 hours at a relatively high intensity are particularly relevant from a carbohydrate-loading perspective.(1)

For even longer competitions, it can also be valuable to start with well-stocked glycogen stores. However, the overall benefit of the extra 100 g of glycogen stored at the start is less decisive, especially since the body is opportunistic and will burn carbohydrates at a slightly higher rate when they are plentiful. If you are active at a low to moderate intensity for several hours, your energy intake during the activity itself becomes much more important for your performance and perceived exertion.

Carbohydrate loading therefore does not eliminate the need to replenish your energy during the event.

For a shorter training session or competition, you don’t need to worry about maximising your glycogen stores.

The simplest approach is to increase the proportion of carbohydrates in your usual meals during the final 1–2 days before the competition.

Eat a little more rice, pasta, potatoes or bread, and consider adding carbohydrate-rich snacks. Spread your intake throughout the day instead of trying to consume everything in a couple of large meals.

Also bear in mind that very high-fibre and filling foods can make it difficult to consume enough carbohydrates. It can therefore be smart to choose more easy-to-digest options during carbohydrate loading, especially if you are prone to gastrointestinal discomfort.

Another thing worth knowing is that your body weight may increase slightly during carbohydrate loading. This is because glycogen is stored together with water, which is completely normal and nothing to worry about.(2) The extra fluid you store will also be used to maintain your fluid balance.

It is a good idea to test this approach before a longer training session before using it ahead of the most important competition of the year.

Before the start, the participants had 400–450 mmol/kg of muscle mass (dry weight) in glycogen stores. They completed a glycogen-depleting session, reducing their levels to approximately 80 mmol. Immediately afterwards, they began replenishment with 8 g of carbohydrate per kg of body weight from carbohydrate-rich foods and a sports drink. During the test, the diet consisted of 80% high-GI carbohydrates, resulting in very rapid replenishment and recovery.

The black bars represent the participants who took creatine. After the first day, the creatine group had replenished 82% more glycogen in their muscles and had already returned to, or even slightly exceeded, their baseline muscle glycogen levels. This elevated glycogen level was maintained over the following five days, meaning that they consistently had more glycogen than the control group.[4]

So—how about adding a little creatine?

Eating 8–12 g of carbohydrates per kilogram of body weight is easier said than done, especially if you weigh a little more or don’t normally eat such large amounts of carbohydrates.

But you don’t need to get all of them from regular food.

An easy way to supplement your diet is to drink some of your carbohydrates. This could be through a carbohydrate drink such as U Loader or, for that matter, by bringing along some extra travel snacks in the car on the way to the start.

U Loader contains isomaltulose (Palatinose) as a carbohydrate source. It has a low glycaemic index and is absorbed more slowly than the carbohydrates in our regular sports drinks. One 80 g serving of U Loader provides 76 g of carbohydrates and can therefore be a convenient supplement when you’re starting to get tired of eating.

But remember that there’s nothing magical about the product itself when it comes to glycogen storage. It’s your total carbohydrate intake that determines how successful your carbohydrate loading is. (1)

So eat your carbohydrates, drink them if that makes things easier, and make sure you arrive at the start with well-stocked energy reserves.