The Glycemic Index
American Institute for Cancer Research
What Is It?
The Glycemic Index ranks carbohydrate-containing foods by how quickly they elevate blood sugar levels. It is measured by comparing the increase in blood sugar after eating 50 grams of carbohydrate from a single food to the increase in blood sugar that occurs after eating 50 grams of carbohydrate from a reference food, either glucose or white bread.
Proponents of the Glycemic Index argue that foods that raise blood sugar quickly – foods that have a "high GI" ranking – stimulate hunger, increase enzymes that promote the storage of fat and reduce the body's ability to burn fat.
Why Is It Controversial?
Critics of the Glycemic Index maintain that it is only a reference tool, and as such has several limitations that cannot account for the kind of complexities that occur outside of a laboratory environment.
What Specific Criticisms are Directed at the Glycemic Index?
The GI of a food is not a fixed, unchanging figure – it varies considerably from person to person. It even varies within the same person, depending upon a host of complicating factors.
The scale used by the GI to measure differences in rate of digestion makes those differences seem larger and more significant than they actually are.
The GI of a food is based upon an arbitrary amount of carbohydrate (50 grams) that may or may not correspond to the amount of food that is typically eaten. Attempts to correct for this built-in abstraction (by calculating the glycemic load) only serve to magnify the abstraction even further.
People don't eat individual foods – they eat meals. Studies investigating the applicability of the glycemic index for meals remain contradictory.
There is still disagreement about how to calculate the Glycemic Index in the first place. Basic questions about the method of calculation, timing of blood sugar testing, and whether to use glucose or white bread as a reference food – along with a host of other factors – still need to be resolved.
Popular Diet Books – as of November, 2003
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For more information, or to contact American Institute for Cancer Research, see their website at: www.aicr.org
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