SPORT NUTRITION

Carbohydrate


All energy, whether it's to play sport or carry out any other activity, comes from three classes of food called macronutrients. These nutrients are better known as carbohydrates, fats and proteins. Each is important - not only to fuel athletic performance but also for overall health and well-being.

Weight for weight carbohydrates contain the least amount of energy out of the three macronutrients. Yet they are the most important type of fuel to an athlete.

During short, intense bouts of exercise (like sprinting), carbohydrate is the only fuel capable of supplying the body with energy quickly enough. In the first few minutes of any activity, it is carbohydrate that almost exclusively meets energy demands. In addition, the ability to repeat a sprint at the end of a game or race, to the same high level as at the start of the game relies, in part, on the body's carbohydrate stores.

Although the body does use fat for lower intensity activity, carbohydrate acts as a "primer" or catalyst for fat to be broken down. Finally, carbohydrates play a key role in central nervous system function. The brain for example, uses glucose almost exclusively as its fuel.

Can diet significantly affect the body's carbohydrate stores?

The average person has about 2000 calories of stored carbohydrate. An overnight fast (8 to 12hrs) and a low-carbohydrate diet can dramatically lower these stores. More importantly, a carbohydrate-rich diet can more than double them. The body's upper limit for carbohydrate storage equates to about 15 grams per kilogram (2.2lbs) of bodyweight. So an 80kg (175lb) person can potentially store up to 1200 grams of carbohydrate or 4800 calories worth of energy - all with just a few dietary modifications.

There are different types of carbohydrates. Understanding what they are and how they affect the body differently, is important to athletes and what they eat before and after a game.


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Monosaccharides
This is the most basic unit of carbohydrate. Examples of monosaccharides include fructose (sugar found in fruit) and glucose (also called blood sugar). Cells can use the glucose found in food directly for energy, while fructose is converted to glucose in the liver.


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Disaccharides
Combine two monosaccharides and the result is a disaccharide. Sucrose or table sugar is a disaccharide and it's the result of combining glucose and fructose. The sugar in milk, lactose, is another disaccharide. The collective name for both monosaccharides and disaccharides is simple sugars. Simple sugars are quickly absorbed by the body and provide a rapid source of energy.

Simple sugars such as fruit and energy drinks are a good food choice to refuel AFTER a game when the body's energy stores are low.


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Polysaccharides
Starch and fibre are both polysaccharides. Starch is the combination of hundreds of monosaccharides joining together. Nutritionists often refer to polysaccharides as complex carbohydrates. Examples include bread, potatoes, rice and pasta. It takes longer for the body to break these complex structures down so they release their energy over a longer period than simple sugars.

Fibre differs from starch in that it cannot be digested and used for energy. It's still an important dietary component though and there is a growing link between lack of fibre and certain degenerative illnesses.

Starchy complex carbohydrates are the best choice BEFORE a game as a pre-match meal.

In Part 5 of this series, we'll cover sample pre and post competition meals and what they should contain. Closely related to the subject of carbohydrates is the Glycemic Index and that's something we'll cover later also.