Glycemic Index

The glycemic index (GI) is a measure that ranks carbohydrate-containing foods according to the blood glucose response produced by a fixed amount of their available carbohydrate. It is determined by comparing the blood glucose response to a test food with the response to an equal amount of available carbohydrate from a reference food, usually glucose .^1,2

In standardized testing, blood glucose is measured over two hours after the test food is consumed. The incremental area under the blood glucose response curve is calculated and expressed as a percentage of the response produced by the reference food in the same individuals. When glucose is used as the reference, it is assigned a GI of 100. A higher GI therefore indicates a greater blood glucose response under these standardized conditions for the same amount of available carbohydrate .¹

GI characterizes a food under specified testing conditions; it does not indicate how much carbohydrate is present in a typical serving. Factors such as starch structure, food processing, physical form, and the presence of other food components can influence carbohydrate digestion and absorption and therefore affect a food's GI .²

Glycemic index is distinct from glycemic load (GL). GI compares foods using equal amounts of available carbohydrate and describes their relative glycemic response under standardized conditions. Glycemic load also incorporates the amount of carbohydrate consumed, so it changes with portion size. Two foods can therefore have similar GI values but different glycemic loads when eaten in different amounts .^2,3