April 2006April 2006
Why Everyone is Counting Them Now
Carbohydrates come from a wide variety of foods - bread, beans, milk, popcorn, potatoes, cookies, spaghetti, corn, and cherry pie.
They also 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.
Carbohydrates were once grouped into two main categories. 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. Things have changed and now the picture is more complicated.
The digestive system handles all carbohydrates in 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. Did you read the November 2005 Randomosity Fitness Newsletter about fiber?
The 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. White bread, for example, is converted almost immediately to blood sugar, causing blood suger to rise rapidly. It's classified as having a high glycemic index.
A comprehensive database about the glycemic index of specific foods is available at http://www.glycemicindex.com/