Glycemic index is a number. It gives you an idea about how fast your body converts the carbs in a food into glucose. Two foods with the same amount of carbohydrates can have different glycemic index numbers. The smaller the number, the less impact the food has on your blood sugar. 1  55 or less = Low (good).2  56- 69 = Medium. 3  70 or higher = High (bad).ring down the overall glycemic index of a meal by combining a high-glycemic index food with foods that have lower ones. Your age, how active you are, and how fast you digest food also affect how your body reacts to carbs.