The Glycemic Index, also known as the GI Diet, is one in which you eat foods according to how they rank on a preset index. The index ranks carbohydrate-containing foods based on their effect on blood sugar level. Foods that rank high on the index value tend to raise your blood sugar quickly. These foods break down quickly in the body and leave you feeling hungry soon after. Low index foods promote a slow to moderate rise in blood sugar and insulin as they're digested. These foods reduce encourage the body to dissolve body fat. The GI Diet is especially popular with diabetics and those suffering from high blood sugar.