WHAT'S THE DIFFERENCE BETWEEN THE GLYCEMIC INDEX (GI) AND GLYCEMIC LOAD (GL)?

The Glycemic Index (GI) has been used for many years as guide to the rate at which carbohydrate content is absorbed into the blood stream for energy, and the effect it has on raising blood sugar levels. The Glycemic Index (GI) is a measure of the degree to which a carbohydrate is likely to raise your blood sugar (glucose) levels.  The scale is 0 to 100 (based on either white bread or glucose), with 0 being low and 100 being high.  The GI compares equal quantities of carbohydrates and provides a measure of carbohydrate quality but not quantity. So the drawback with GI ratings is that they are not based on commonly-consumed portion sizes of foods.
 
For example, only about 7% of a carrot is made up of are useable carbohydrates. But because a 50g carbohydrate content is employed as the standard measure for a GI rating of individual foods to show how fast blood sugar level are raised, a larger than normal food portion is used for the GI calculation.  In the case of carrots, for example, the amount is equivalent to 1.5lbs - far more, of course, than people normally eat as a snack or part of a meal. 
 
As a result, the GI rating often overstates relatively small carbohydrate content in a food item like a carrot.
 
The reverse is also true, i.e. the glycemic effects of foods containing a high percentage of carbs like bread, can often be understated under the GI system.
 
Therefore we recommend using the Glycemic Load index with calculations based upon realistic food portions. GL ranks food according to the effects of actual carbohydrate content in a standard serving size of food.

Glycemic Load (GL) index

In 1997, Harvard University scientists introduced the concept of Glycemic Load (GL).  This measure gives a more accurate reflection of the blood sugar effects of a standard food portion.  In short, the GL of a typical serving of food is the product of the amount of available carbohydrates in that serving and the glycemic index of that food. 

In practical terms, the higher the GL of a food, the greater the expected rise in blood glucose and the greater the adverse insulin effects of the food.  Foods with a GL of 10 or below would be presumed to be less detrimental to health, while those with a GL of 20 and above would have more detrimental effects.  Long term consumption of foods with a high glycemic load appears to be linked to a greater risk of obesity, diabetes, and inflammation.  These, it also now appears, may even have negative effects on the brain that we are only beginning to understand.
 
We have chosen to base our program on the glycemic load, as this is more reflective of the actual load of carbohydrates. Another reason to use Glycemic Load is that Glycemic Index can be deceptive for certain foods, especially those that contain added fructose (which is an unhealthy sugar for people with diabetes).   

About Fructose

Fructose has become the most prevalent sweetener in the diet because it is sweeter than sucrose (common table sugar).  It is often recommended because, on the Glycemic Index, it measures a paltry 32 (out of 100).  This would put fructose among the items with a "low glycemic index."

But we’ve been fooled for years by fructose and its low Glycemic Index.   It turns out that consuming fructose has a dark side for all organ systems.  Scientists have found that eating fructose actually creates insulin resistance. Fructose also contributes to abnormal sugar-protein reactions called "glycation," which damages a large array of structural (ligaments, cartilage, muscle) and functional (enzymes, neurotransmitters) proteins throughout the body. 

Source: This excerpt is with permission of Michael A. Schmidt, PhD and Frog Books, Ltd. Berkeley, CA
 

Glycemic Load of Common Foods

* Compared with pure glucose, which is assigned a glycemic index of 100.

Sources: This table is adapted with permission from: "International tables of glycemic index and glycemic load values: 2002," by Kaye Foster-Powell, Susanna H.A. Holt, and Janette C. Brand-Miller in the July 2002 American Journal of Clinical Nutrition, vol. 62, pages 5-56. The complete list of the glycemic index and glycemic load for 750 foods can be found at: http://www.ajcn.org/cgi/content/full/76/1/5.

Updated (where applicable) with current values from the "Home of the Glycemic Index" - the official website for the glycemic index and international GI database which is based in the Human Nutrition Unit, School of Molecular and Microbial Biosciences, University of Sydney: (http://www.glycemicindex.com/). Last modified: December 13, 2005.