Glycemic index (GI) measures the effect on the body produced by carbohydrates in different foods. It gives an indication as to how quickly carbohydrates in different food are absorbed, and the resulting effect on blood sugar. GI can range from 0-100, and generally speaking, low GI foods have a GI below 55, while higher GI foods (those that can increase blood sugar quickly) are those with GI greater than 55. The GI of many common foods and more information on GI can be found through the links below.
https://extension.oregonstate.edu/sites/default/files/documents/1/glycemicindex.pdf