Glycemic index, also called glycaemic index (GI), is a ranking system for carbohydrates based on their effect on blood glucose levels in the first two hours after eating. It compares carbohydrates gram for gram in individual foods, providing a numerical, evidence-based index of post-meal (medically called: postprandial) glycemia. The concept of glycemic index was developed by Dr. David J. Jenkins and colleagues in 1981 at the University of Toronto.