Until the end of the 20th century, science related to carbohydrates as either simple or complex. Most refined foods were considered simple carbs and whole grains and starchy foods in their natural state were generally considered complex carbohydrates. Today, there is a much better understanding how carbohydrates affect the body; the glycemic index and glycemic load of carbohydrate-based foods provide information so you can make healthier food choices.
Glycemic Index
Most carbohydrate-based foods are broken down into glucose, which provides energy to the body's cells, during digestion. Through the development of the glycemic index, scientists determine both how rapidly a food raises the blood glucose -- blood sugar -- level after a meal and to what degree. This is done by comparing a 50 g sample of the desired food against a like amount of a control food, either white bread or pure glucose. The resulting number is the comparison of the desired food's effects versus the control food's effects on the volunteer's blood glucose levels. If the desired food affects blood glucose levels to nearly the same degree as the control food, the desired food will receive a high glycemic index rating. If blood glucose levels are affected minimally, the desired food will receive a low glycemic index rating.
Glycemic Load
The glycemic index rating only tells part of the story when it comes to knowing exactly how a food affects blood glucose levels. The glycemic rating indicates the potential of a food to affect blood glucose levels, while the glycemic load tells the "whole story" of the food portion you are eating. Glycemic load is determined by the grams of carbohydrate in a food portion multiplied by that food's glycemic index rating, then dividing by 100. In this manner, scientists are able to determine both the quantity and quality, carbohydrate-wise, of a food portion, meal or entire day's food.
Considerations
Only carbohydrate-based foods have glycemic index and glycemic load ratings. Although many foods with a low glycemic index rating have lower calories than their higher glycemic index counterparts, a food or portion of that food may also have protein or fat grams that will not be reflected in the glycemic index rating. Foods with a low glycemic load -- 10 g or less per serving -- such as beans and legumes, high-fiber fresh fruit and vegetables and bran cereal also have other nutrient value not measured by the glycemic index.
Uses
A diet based on the glycemic index is useful for those with diabetes. It may also be useful for those with metabolic syndrome or insulin resistance, because when blood glucose levels are raised more slowly and moderately, the beta cells of the pancreas need only release small amounts of insulin in response, rather than the large amounts of insulin required for rapidly rising and high blood glucose levels.
Some of the commercial weight-loss diets are based on the glycemic index. Although there are not yet conclusive scientific studies to prove a low glycemic index diet promotes weight loss, it stands to reason your body functions most effectively, including metabolizing food and making best use of cell energy, when your blood glucose levels are stable and within normal limits.
