The glycemic index resulted from the work of scientists who studied volunteers who ate 50 g of carbs and a control food such as white bread. Blood samples taken from these subjects determined blood glucose levels prior to eating and then at intervals over several hours after eating. They applied the data they obtained to many foods using various calculations. Then they compiled a list of foods and their corresponding value based on how fast or slow the food became glucose in the body after eating. Generally the foods with low values took longest to turn to sugar and therefore are easiest on the pancreas. This list of glycemic values gave birth to the glycemic index.
ROLE OF FIBER
Nutritionists soon realized that the index did not take into consideration the actual amount of carbs in the foods. The missing piece, the amount of fiber, needed consideration. In answer to this need, the concept of glycemic load evolved. The glycemic load takes into account the amount of fiber contained in the food. Fiber has shown the ability to slow the metabolic processing of carbohydrates, making the carbs less offensive to the body. Therefore, a food that has a moderate GI value but contains lots of fiber may actually have a low glycemic load.
You can calculate the glycemic load of a food or of an entire meal by using this simple equation. First look up the food in the glycemic index, which is available as a paperback. Take its glycemic index value and multiply it by the amount of available carb grams of the food minus the amount of fiber grams of the food. Now divide the answer by 100, and you have the glycemic load of that food. Do this for all the foods in a meal and add the results together. This gives you the glycemic load of the entire meal. Mathematically the equation looks like this: (GI) x (g of carbs – g of fiber) ÷ 100.
A 1-cup, 225-g serving of bananas has a GI of 52 and a carbohydrate content of 51.4 g. It also has 5.9 g of fiber, which you subtract from the carb content of 51.4 g. With this reduction you now have 45.5 g of carbs. Plug the numbers into the equation. 52 x (51.4 – 5.9) = 45.6 divided by 100. These bananas have a glycemic load of 24, which represents a low and desirable value. You can find the fiber content of the food on its package if it’s a processed food.