Glycemic index (also glycaemic index, GI) is a ranking system for carbohydrates based on their immediate effect on blood glucose levels.
It compares carbohydrates gram for gram in individual foods, providing a numerical, evidence-based index of postprandial (post-meal) glycemia.
Carbohydrates that break down rapidly during digestion have the highest glycemic indices.
Such carbohydrates require less energy to be converted into glucose, which results in faster digestion and a quicker increase of blood glucose.
Carbohydrates that break down slowly, releasing glucose gradually into the blood stream, have a low glycemic index.
A lower glycemic index suggests slower rates of digestion and absorption of the sugars and starches in the foods and may also indicate greater extraction from the liver and periphery of the products of carbohydrate digestion.
Additionally, a lower glycemic response equates to a lower insulin demand, better long-term blood glucose control and a reduction in blood lipids.