The glycemic index measures the increase and decrease of the blood sugar level after the diabetic has eaten. This is done between two and three hours after a meal and the index describes the ranking of carbohydrates and what their effect is on the blood glucose level.

This is important for the diabetic to know, because foods need to be monitored as well as the blood glucose level and food is the main contributor to whether the blood sugar level is normal, high or low. This is also a way to monitor weight gain or loss, and while that is important for everyone it is extremely important for the person with diabetes as this can help to cause other complications.