Glycemic index

The glycemic index, or GI, compares how strongly different carbohydrate foods raise blood sugar. To measure it, healthy volunteers eat enough of the food to provide 50 grams of available carbohydrate, and their blood glucose is followed for two hours. The area under that curve is compared with their response to the same amount of pure glucose, which serves as the reference at 100. Foods scoring 55 or less are classed as low GI, 56 to 69 as medium and 70 or more as high.

Low-GI foods, such as most legumes, oats, barley and many whole fruits, are digested and absorbed slowly, so blood glucose and insulin rise gently. High-GI foods, such as white bread, white rice, potatoes and many processed cereals, are absorbed quickly. A food's GI depends on its fiber and fat content, its ripeness, how much it has been processed and how it is cooked; pasta cooked al dente scores lower than soft pasta. Foods with little or no carbohydrate, such as meat and oils, have no GI value.

GI is used in managing diabetes mellitus and in nutrition research. Because it ignores portion size, a related measure, glycemic load, combines GI with the amount of carbohydrate in a typical serving.