The body is mostly made up of water (60%), proteins, lipids, minerals and carbohydrates. * All these elements come from food and are either used to provide the necessary energy for the body to function properly, or combine to form the tissues which make up organs.
Carbohydrates: a source of energy.
Carbohydrates, which are also called "sugars" or "hydrates of carbon" are our main source of energy.
Once digested, they're stored in the muscles and liver, in varying amounts, in the form of glycogen. The energy provided by carbohydrates is equivalent to 4kcal/g.
There are two types of carbohydrates. In the past, these were divided into 2 distinct categories:
- simple carbohydrates (or fast-release carbs): sucrose, fructose, glucose, which you find in fruit, sugar, fizzy drinks etc.
- complex carbohydrates (or slow-release carbs): starch is present in cereals, leguminous plants, potatoes etc.
Do we still talk about slow-release and fast-release carbs?
Today, we classify carbohydrates by glycemic index (GI). This is tool which measures the speed of carbohydrate digestion. To determine if a food has a high or low GI rating, we compare it to glucose = 100.
The GI of a food is dependent on the type of carbohydrate it contains (fast-release or slow-release), the presence of other molecules (fibres, proteins, lipids), the method of cooking and the different industrial processes involved in production. So the notion of fast-release, meaning simple carbs, and slow-release, meaning complex carbs, is no longer relevant.
A GI rating is considered high when above 70, moderate when between 55 and 70 and low when below 55.
How much carbohydrate do we need?
Carbohydrates provide approximately 50-60% of our total daily energy intake. The recommended intake is approximately 6g/kg of body weight/day. Sugars with a high GI rating should not account for more than 10% of the body's total daily energy intake.
If sedentary, you need to be careful when eating sugar as your muscles' reserves of glycogen will already be full. The additional supply of glucose will then, most likely, be stored in the form of fat.
Conversely, carbohydrates with a high GI rating are an extremely important source of nutrition as they are used more slowly. For athletes, carbohydrates with a low GI rating constitute an important part of their overall diet.