How The Glycemic Index (gi) Is Determined

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HOW THE GLYCEMIC INDEX (GI) IS DETERMINED

The Glycemic Index (GI) is a physiological measure of how fast, and to what extent, a carbohydrate food affects blood glucose levels. The GI uses the blood glucose response (BGR) to GLUCOSE as the point of reference. The GI of a specific food is determined by comparing the BGR of that food with the BGR of GLUCOSE. GLUCOSE is absorbed quickly from the small intestine and generally causes the greatest and most rapid rise in blood glucose. Usually, 50 grams of carbohydrate (the equivalent of 3 tablespoons pure glucose powder) is used to establish the Glucose Base or Index reference for a specific test person. A value of 100 would be allocated to the BGR of GLUCOSE for that person. In practice, the BGR of GLUCOSE would be tested at least three times in each test person to ensure an accurate reference for the other tests.

The BGR measurement is done by testing the actual blood glucose level of the test person every 15 minutes for a period of 3 hours. The glucose level readings are plotted on a chart or graph. The area under the curve, which indicates the rise and fall of BGR, is calculated and represents the absolute BGR of the specific food for that specific test person. To calculate the GI of the food the absolute reading is expressed as a percentage of the absolute reading of the BGR of glucose. In order to ensure accuracy the BGR of eight to twelve people is measured to determine the GI of a certain carbohydrate. The average of the group for a specific food is used as the GI value of that food.

To determine the GI of a specific food, e.g. potatoes, an amount containing 50 grams of carbohydrate is given to a test person to eat. Thus, in the case of boiled potatoes, a volunteer would be given 250 grams of potatoes which supplies 50 grams of carbohydrate.