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How is Glycemic Index Measured - Glycemic Index - How Foods Raise Blood Sugar Compared to Glucose

How is Glycemic Index Measured

Diet Information - What is the Glycemic Index

How is Glycemic Index Measured

The glycemic index (GI) is a measurement of the rate at which carbohydrate-containing foods raise blood sugar (glucose) levels. See also Glycemic Load

GI Food Measurement Tests

The glycemic index of a food is measured under strict test conditions. To measure glycemic index, portions of a carbyhodrate food are fed to a panel of volunteers who then give blood samples at regular intervals over 2 hours for determination of glucose levels.

Measuring Glycemic Index

  • The GI value of a food is assessed by giving 10 or more volunteer subjects a serving of the food containing 50 grams of digestible (available) carbohydrate.
  • For example, to test boiled spaghetti the subject is given 200g of spaghetti, which supplies 50g of carbohydrate.
  • To test how the food raises blood sugar levels, a sample of blood is taken from each subject every 15 minutes during the first hour and thereafter every 30 minutes. The blood sugar level of these blood samples is measured and recorded.
  • The blood sugar level is plotted on a graph and the area under the curve is calculated using a computer program. The subject's response to the food being tested is compared with his/her blood sugar response to 50g of pure glucose. (Glucose is the reference food and the testing of glucose on the subject's blood sugar levels is done on a separate occasion.)
  • The average blood sugar response from 8-10 people will determine the glycemic index (GI) value of that food.

High, Low and Intermediate GI Foods

Glucose is assigned an arbitary GI of 100. Foods with GIs below 55 are considered to have a low glycemic index. Numbers above 70 indicate a high glycemic index, and numbers between 55 and 70 are intermediate.

Effects of High GI Foods

Foods with a high GI score contain rapidly digested carbohydrate, which produces a large rapid rise and fall in the level of blood glucose. In contrast, foods with a low GI score contain slowly digested carbohydrate, which produces a gradual, relatively low rise in the level of blood glucose.

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