To further add to Karen's reply: "The glycemic index (or G.I.) was developed to rank foods based on their immediate effect on blood sugar levels. Carbohydrate foods that break down quickly during digestion have the highest G.I. values because the blood sugar response is fast and high. Conversely, carbohydrates that break down slowly, releasing glucose into the bloodstream, have low G.I. values. The substance that produces the greatest rise in blood sugar levels is pure glucose itself. The glycemic index of pure glucose is set at 100 and every other food ranked on a scale from 0 to 100 according to its actual effect on blood sugar levels." from the Glucose Revolution.