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Wednesday, 14 January 2015 20:48

Carbohydrates are an important fuel for athletes

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Carbohydrates are an important fuel for athletes ©travellight shutterstock

Nowadays you read and hear everywhere that low-carbohydrate diets are the best to lose weight, have a healthy diet, and even can improve sports performance. However, there is no scientific evidence for these claims. On the other hand, there is lots of scientific evidence that a high-carbohydrate diet is crucial for good sport performance, and low glycogen levels can even impair your sports performance. When exercise intensity increases, carbohydrates are the main fuel for athletes.

Unfortunately there are many recreational and competitive athletes who are not familiar with the importance of carbohydrates for training and competition. Often they restrict their carbohydrate intake because a training partner has advised it to them, or they read something about it in a book, a magazine or on the internet.

Calories are still important

High protein diets, which are also typically high in fat, suppress appetite, this ensures that this type of diet is easier to follow. In addition, a low carbohydrate diet produces less insulin with each meal. Lower insulin levels may lead to reduced fat storage and an improved regulation of glucose in the blood. It should be noted that most research on glucose and insulin regulation, weight loss, and the response to various diets is often performed on people with obesity and type 2 diabetes, and not on athletes or active individuals.

Many of these diets restrict eating bread and grains but let you eat as much fruits and vegetables as you want. As a result, the amount of carbohydrates in the diet are very low. There is a lot of research on the advantages and disadvantages of low-carbohydrate diets. Ultimately, it is more important that your calorie expenditure is higher than your calorie intake to lose weight.

Fats don’t provide enough energy during intense efforts

For athletes, carbohydrates are very important. When the intensity of the effort increases more ATP is produced. ATP stands for adenosine triphosphate and is the main fuel of the body. During exercise carbohydrates and fats are used for ATP synthesis, where fats are the main substrate during low intensity exercise. At higher intensities, from 50-60% of VO2max, ATP production increases and fats can not provide enough energy to meet the energy demand, therefore the amount of glucose that is used for the production of ATP increases. Although more energy can be extracted from fats, carbohydrates provide energy at a faster rate and are therefore necessary for ATP synthesis at higher intensities.

Even at low intensities carbohydrates are used as a fuel, so it is a misunderstanding that fats are the only fuel used during low intensity exercise. At higher intensities are carbohydrates almost the only fuel used for ATP synthesis, this is why carbohydrates are so important for athletes. Fats simply can not provide the energy fast enough to meet the demands of heavier exercise.

Carbohydrates are stored as glycogen

In the body are carbohydrates stored in the form of glycogen. Compared to the amount of fat that can be stored, the storage capacity for carbohydrates is very limited. About 300-400 gram is stores in the muscles, about 60-120 grams in the liver, and blood contains a small amount of carbohydrates in the form of glucose.

It is therefore important to have enough glycogen reserves before you start exercising and also consume enough carbohydrates during exercise that lasts longer than 90 minutes.

A low carbohydrate diet can cause overtraining

Fatigue and decreased performance are partly caused by depleted glycogen stores. Even for athletes with a healthy and varied diet it’s not always easy to eat enough carbohydrates, because the reserves are limited and the expenditure during exercise is high.

When glycogen stores are low or depleted the body starts using protein and amino acids to produce glucose. Because proteins are the building blocks of muscles, this process will damage the muscles. As a result the damaged muscles can store and synthesize less glycogen. If this happens, the athlete could enter a vicious cycle leading to overtraining and a decrease in performance.

The amount of carbohydrates for training and competition

The amount of carbohydrates you require are different for each individual. During low intensity efforts you need fewer carbohydrates, but for low intensity efforts during a long period of time you will need a considerable amount of carbohydrates. Efforts at a higher intensity are almost entirely dependent on carbohydrates so you need large amounts of carbohydrates.

For people following a low carbohydrate diet, the carbohydrate intake is generally limited to less than 100 grams per day. General guidelines for carbohydrate intake for athletes or active individuals are very individual. These range from 3 grams of carbohydrate per kilogram of body weight per day for people who participate in short efforts  (<1 hour) at a low intensity, and up to 12 grams of carbohydrate per kilogram of body weight per day for athletes participating in prolonged activities (4-5 hours per day) at moderate to high intensity.

Part of this daily intake is consumed during exercise, for which clear guidelines exist.

  • <45 min no carbohydrate intake needed
  • 45-75 min at higher intensity, small amounts including mouth rinsing
  • 1-2.5 hours endurance training including "start and stop" activities 30-60 grams of carbohydrate per hour
  • > 2.5 hour ultra endurance events >90 grams of carbohydrate per hour
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