The Glycemic Index was developed in the early 1980s to measure how much your blood sugar increases in the two or three hours after eating a particular food. Foods that are high in carbohydrates tend to raise the level of glucose in your blood more than foods that are high in fat or protein.

The Glycemic Index is central to the South Beach diet, which encourages its participants to focus on low GI foods. The South Beach diet claims that low GI foods (those with a GI less than 55) are the healthiest for your body, as they cause only a gradual rise in blood sugar. High GI foods (those with a GI higher than 70 cause your blood sugar (and your insulin levels) to rise quickly. Intermediate GI foods are those with a GI between 55 and 70.

Related to the Glycemic Index is the concept of the Glycemic Load. While the GI measures how quickly your body converts a carbohydrate into glucose, it does not indicate the quantity of a carbohydrate in a particular serving of food. The Glycemic Load is essentially the GI multiplied by grams of carbohydrate in a particular food.