Glycemic Index (GI) & Glycemic Load (GL)

Glycemic index  ( GI ) is a measure of how quickly blood glucose levels rise after eating a particular type of food.   The GI estimates how much each gram of available carbohydrate in a food raises a person’s blood glucose level following consumption of the food, relative to consumption of pure glucose.  Glucose, has a GI of 100, as the defining standard for other foods.   

Foods with carbohydrates that break down quickly during digestion tend to have a high GI, while food with carbohydrate that break down more slowly have a lower GI.  Thus a high GI equates to a higher insulin demand.

GI was invented by Thomas Wolever and David Jenkins of the University of Toronto in 1981.  GL was created by researchers of Harvard University in 1997.

The amount of carbohydrate food consumed too has to be considered.  The glycemic load ( GL ) estimates how much carbohydrates in the food is in the food, and how much each gram of carbohydrate in the food raises blood glucose level.  GL is derived by multiply the food’s GI with food’s carbohydrate content and divided by 100.

GL =  [ GI x food’s carbohydrate (g) ] / 100

1 unit of GL approximates the effect of consuming 1 g of glucose.

Example : Watermelon

GI _(watermelon) = 72

100g watermelon has a 5g of carbohydrate and 98g of water.

GL _(watermelon) = ( 72 x 5 ) / 100 = 3.6

Classification

	GI	GL
High	> 70	> 20
Medium	56 - 69	11 - 19
Low	< 55	< 10

http://www.health.harvard.edu/newsweek/Glycemic_index_and_glycemic_load_for_100_foods.htm