Carbohydrates are a combination of oxygen, hydrogen and carbon and are the human body’s most common source of energy. Carbohydrates are often categorized into two groups: simple carbohydrates, which are quickly absorbed by the body and are found in foods such as refined sugars, milk and some fruits, and complex carbohydrates, which are fiber-rich and more slowly digested.
In 1981 David Jenkins and Thomas Wolever developed the Glycemic Index at the University of Toronto. The Glycemic Index is a measure of how fast a food raises the blood-sugar level as compared to table sugar or white bread. The higher the Glycemic Index value a food has, the faster the blood-sugar level is raised. The amount of fiber found in a food greatly lowers its Glycemic Index score. White bread, for example, which contains almost no fiber, rates high on the Glycemic Index, while fiber-rich whole-grain bread has a much lower score.
Dietary fiber consists of an intricate grouping of carbohydrates found in plant- based foods. Dietary fiber is not converted to glucose and contributes no calories, but adds bulk, causing a feeling of satiety, or fullness. Fiber is grouped into two categories: soluble and insoluble. Soluble fiber absorbs water and converts it into a gelatinous substance during digestion. This process traps carbohydrates and slows the absorption of sugar into the body. Insoluble fiber does not absorb water, but speeds the passage of foods through the digestive system.
Carbohydrates and fiber interact to play an important dietary role. When counting carbohydrates, it is important to note that total carbohydrates and net carbs are not the same. Net carbohydrate intake refers to carbohydrates absorbed and digested in the intestinal tract. Since fiber is indigestible, it does not count toward the net carb intake. To calculate the net carbohydrates in a food, subtract the total amount of fiber grams from the total carbohydrate grams. The resulting sum is the net carbohydrate content of that food. For example, if a food contains 17 grams of carbohydrates and 6 grams of fiber, the food's net carbohydrate total is 11 grams.