glycaemic index

glycaemic index

A measure of the effect a given food has on blood sugar levels, expressed in terms of a comparison with glucose, which has a value of 100. Fast-releasing foods that raise blood sugar levels quickly are high on the index, while slow-releasing foods, at the bottom of the index give a slow but sustained release of sugar.

glycaemic index (GI)

a ranking from 0–100 of CARBOHYDRATE-containing foods, according to their effect on blood GLUCOSE levels after being eaten. GI was introduced by David Jenkins and co-workers in 1981. Generally the blood glucose response (BGR) to glucose is taken as the reference (although some researchers use white bread as the reference), with a GI value of 100 and other foods are ranked in comparison to this. The GI value of a food is determined from the BGR following ingestion of a portion containing 50 g carbohydrate, expressed as a percentage of the BGR of 50 g glucose ingested by the same test person: GI = incremental area under the glucose response curve (0–2 h) for the sample divided by incremental area under the glucose response curve for the reference x 100. The index indicates whether the available carbohydrate (‘glycaemic carbohydrate’) in the food raises the blood glucose dramatically (high GI, 70 or more), moderately (moderate GI, 56–69) or a little (low GI, 55 or less). This depends on how rapidly the carbohydrate is digested and absorbed into the bloodstream. The GI depends on the nature of the food itself, for example the form of carbohydrate it contains, the fibre and fat content, and the extent of processing /cooking. Compare GLYCAEMIC LOAD.