Carbohydrates are to be found in many foods, like beans, bread, milk, potatoes, popcorn, spaghetti, biscuits and soft drinks. They are available in many forms; the most common and widely consumed forms are fibres, sugars, and starches.
Each carbohydrate is basically a sugar molecule, a straightforward union of hydrogen, carbon and oxygen. Fibres and starches are basically sugar molecule chains; some of these contain several hundred sugars.
Carbohydrates have traditionally been grouped into two main types. Simple carbohydrates include sugars like fruit sugar (fructose), grape or corn sugar (glucose or dextrose), as well as table sugar (sucrose).
Complex carbohydrates consist of three or more linked sugars. It was thought that complex carbohydrates were the most healthy to eat, with simple carbohydrates being less good for the body. It is now considered that the situation is more complicated than that.
The digestive system handles each type of carbohydrate in more or less the same way; it breaks them down or tries to break them down into single sugar molecules, as they then become small enough to cross into the bloodstream.
In addition, the digestive system converts most digestible carbohydrates into glucose (or blood sugar), as cells are designed to use blood sugar as an energy source.