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Sunday, June 8, 2008

GI? GL? Gee Whiz!

Every now and then, the terms GI and GL are thrown around in the press, but I wonder how many people out there understand what on earth they are talking about. The consumption of all foods causes a glycemic response in the body; that is a change in the level of glucose in the blood. GI and GL are related to this response.

GI stands for glycemic index and is a numerical ranking system rating carbohydrates on their glycemic response. It is based on a scale from 0 to 100 where straight glucose equals 100. Generally a number of 70 or greater is considered high and a number of 55 or lower is considered low.

GL stands for glycemic load and is calculated as GI /100 X net carbohydrates (net carbs = total carbs minus fiber). Glycemic load is calculated because the body's glycemic response is dependent on both the type and quantity of carbohydrate consumed. A GL of 20 or greater is considered high and a GL of 10 or lower is considered low.

Information on GI (and GL) is still really limited in availability because each and every food must be tested. The glycemic index of a food is still determined by studies on human test subjects who fast overnight and are then given a fixed portion of food and are then subjected to blood glucose testing at set intervals to measure their body's response. The average of the test subjects is then calculated and determined as the GI for that food. Obviously this is an expensive and time intensive process!

And even if you possess the GI value for a food, there are a number of factors that affect the actual glycemic response in your body. The ripeness of a fruit or vegetable causes a dramatic change in the glycemic response, as does preparation of a food. The more easily and quickly a food can be digested, the faster and greater the glycemic response (for example: pasta cooked 15 minutes versus 10 minutes has a higher GI value). In addition, GIs are determined on single foods at a given quantity but that's not how we eat. We eat varying amounts of food in combination with other foods; protein, fat and fiber all have an effect on glycemic response. And lastly, each and every one of us converts carbohydrates to glucose at different rates; no one has the exact same insulin response.

So, what to make of GI and GL? Well, they are useful to a point, especially if you have blood sugar issues. They can certainly help you to make food decisions to help you control your insulin response, but they aren't foolproof or written in stone. Don't rely on them solely for making food choices, but being food literate is always smart!

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