The glycemic index
The glycemic index (GI) ranks carbohydrate foods against glucose, based on how quickly they affect blood glucose levels. Glucose is given a value of 100, and other foods are ranked relative to this.
The relative ranking is unlikely to change over time, but it may vary somewhat in daily use. The effect a food has on blood glucose levels can be altered by ripeness, cooking time, fiber, and fat content. Use of a continuous blood glucose monitor can allow the creation of a personal glycemic index. A personal index will require trial and error, but can help you improve and maintain blood glucose control.
Foods with higher rankings are good choices for combating lows and for use with exercise. Fast carbs raise blood glucose during exercise and speed the restoration of glycogen stores following exercise. Foods with lower rankings are better choices for maintaining day-to-day control. Slow carbs minimize unwanted spikes after meals and lessen the drop in blood glucose caused by long periods of activity.
Mixing foods with different glycemic indices will result in an intermediate effect, so it is beneficial to count carbs while using the glycemic index.
A food’s glycemic load is found by multiplying its glycemic index by the number of grams of carbohydrate in a single serving. Glycemic load makes the glycemic index more practical, because a small portion of a high glycemic index food can raise blood glucose as much as a large portion of a low glycemic index food. Portion size must be considered in addition to glycemic ranking.
Sources of information for glycemic index and glycemic load
- http://www.glycemicindex.com/ — Maintained by the University of Sydney, this website claims to be the official website for the glycemic index and international GI database. You can search for foods based on name, glycemic index, and glycemic load.
- http://www.gisymbol.com/ — Home of the Glycemic Index Foundation, formed in 2001 by the University of Sydney and JDRF Australia.
- http://ajcn.nutrition.org/content/76/1/5.full.pdf+html – Article published in The American Journal of Clinical Nutrition, in January 2002.