Quite simply: A carbohydrate with a high glycemic index (high GI) breaks down quickly during digestion and therefore releases glucose into the bloodstream rapidly. Some common foods with a high GI rating include white bread, white rice, corn flakes, crackers and most sugary and/or highly processed snack foods.A carbohydrate with a low glycemic index (low GI) breaks down more slowly therefore causing a much slower and more gradual release of glucose into the bloodstream.ome common foods with a high GI rating include white bread, white rice, corn flakes, crackers and most sugary and/or highly processed snack foods. A carbohydrate with a low glycemic index (low GI) breaks down more slowly therefore causing a much slower and more gradual release of glucose into the bloodstream.