The glycemic index, or GI, rates foods on a scale of 1 to 100 based on how they affect your blood sugar. Low-glycemic index foods have a glycemic index value less than 55. These foods take a while to break down in your gut, resulting in a steady increase in blood sugar. Foods with a glycemic index over 70 are high on the scale and cause your blood sugar to surge and then suddenly drop. If you are managing diabetes or following certain weight-loss diets, selecting low-glycemic index breads may help keep your blood sugar under control.