The GI is used to measure the effect of carbohydrates on blood sugar levels. High-GI foods contain sugars and most starches. They are digested quickly and cause a spike in blood sugar. The GI of glucose, for example, is 100.
Low-GI foods are digested and absorbed slowly by the body, resulting in a gradual increase in blood sugar and insulin levels. Foods with a low GI include those high in fiber and are sometimes called “good carbs.”