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What does “carbo-loading” mean?

Carbohydrate loading, also known as “carbo-loading” or “glycogen loading” is a term used to describe a period of high carbohydrate eating that maximises the body’s glycogen stores in preparation of an endurance event.

Why is it important?

In a long distance event like a marathon, your body derives energy from converting both glycogen (stored carbohydrates) and fat to fuel. However, fat is not as efficient form of energy, since your body has to work harder to gain access to it and burn it. So, when our muscles run out of glycogen and fat becomes the major fuel source, we often experience the infamous state of “hitting the wall”, a type of fatigue when the body has to significantly slow down as it turns fat to energy.

By increasing the amount of carbohydrates in your diet several days prior the race, you can increase the amount of glycogen stored in your muscles to 50% or even double it. This extra supply at the beginning of the even may improve your performance by 2-3%, allowing you to exercise at your optimal pace for a longer time, and even result in a faster finish.

What does carbo-loading involve?

The initial strategy (classic approach) known since the 1980s was aiming to fully deplete the body’s glycogen stores over the last week pre-race by hard training and manipulation of the carbohydrate intake (a low carbohydrate intake of 10% of total calories for the first 3 or 4 days and a really high carbohydrate diet of up to 90% of total calories for the last days before the race). However, training at such high intensities may not be welcomed right before a big race, whilst following an extremely low carbohydrate diet can result to dizziness, lack of energy, gastrointestinal disturbances and an increased risk of injuries.

Over the last few years, the scientific data show that you can achieve similar benefits on glycogen storing by maintaining a normal diet of 55- 60% carbohydrates during the preparation period and increasing your carbohydrate intake to 70% of the total calorie intake 2-3 days prior the event and on the race day.

Practical application

  • If you are an experienced athlete, a 2-day protocol can be sufficient to maximise your muscle glycogen stores, but for a beginner it might be a good idea to allow 3 days to reach your goals instead.

  • Increase your carbohydrate intake so that you consume about 7-10 grams of carbohydrates for every kilogram of your body weight (eating more may lead to extremely high muscle glycogen stores which may be broken down faster during the race and lead to a faster depletion). For a 70kg runner that is estimated to 500-700grams of carbohydrates in the day.

  • Simply eating more carbohydrates in your diet will result in an increase of your weight- not ideal for right before your event. To avoid this, try to reduce the amount of fat you are consuming accordingly so that you do not increase your daily calorie intake. Avoid high- fat foods such as butter, creamy sauces and cheese, preferring a tomato sauce for your pasta or plain honey for your toast instead of butter.

  • Your protein intake should still be sufficient to cover your daily needs, but eating higher amounts of protein right before an endurance event doesn’t seem to add any further benefit in muscle strength. You can and should eat a small serving of low-fat protein such as chicken or turkey, yogurt and egg.

  • The type of carbs (simple – sugar, or complex – starch) you consume seems not to be important; the best approach would be to eat a variety of them simply in a larger proportion than you used to, maintaining, however, your total energy intake in the same level.

  • Beware of eating plenty of foods that are high in carbs but also high in fibre, such as fruits and whole grain products, since these may cause some gastrointestinal issues and stomach trouble during the race. Instead, prefer white bread and cereals, peeled fruits and juices to reduce your fibre intake. It would also be wise to restrain form trying new products at this period.


Jeukendrup and Gleeson Sports Nutrition Human Kinetics Champaign IL, 2010

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