 |
|
Carbohydrates -
Carbohydrates form one of the three macro-nutrient categories; proteins and fats are the other macro-nutrient categories. Carbohydrates come in a variety of forms. The most common and abundant are sugars, fibers, and starches. The basic building block of a carbohydrate is a sugar molecule, a simple union of carbon, hydrogen, and oxygen. Starches and fibers are essentially chains of sugar molecules. Some contain hundreds of sugars. Some chains are straight, whereas others branch wildly.
Carbohydrates were once grouped into two main categories: simple and complex. Simple carbohydrates included sugars such as fruit sugar (fructose), corn or grape sugar (dextrose or glucose), and table sugar (sucrose).
Complex carbohydrates included everything made of three or more linked sugars. Simple sugars were considered bad and complex carbohydrates good. However, the picture is much more complicated than that. The digestive system handles all carbohydrates in much the same way - it breaks them down (or tries to break them down) into single sugar molecules, since only these are small enough to cross into the bloodstream. It also converts most digestible carbohydrates into glucose (also known as blood sugar), because cells are designed to use this as a universal energy source.
Fiber is an exception. It is put together in such a way that it can't be broken down into sugar molecules, and so passes through the body undigested.
The Glycemic Index
A new system for classifying carbohydrates calls into question many of the old assumptions about how carbohydrates affect health. This new system, known as the glycemic index, measures how fast and how far blood sugar rises after you eat a food that contains carbohydrates.
For example, white bread is converted almost immediately to blood sugar, causing it to spike rapidly. It's classified as having a high glycemic index. On the other hand, brown rice is digested more slowly, causing a lower and more gentle change in blood sugar. It has a low glycemic index.
|