How is Glycemic Index Measured?
Blood Glucose Levels After Eating 50g Carbs in Foods

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How is Glycemic Index Measured?

The glycemic index of a food is measured under strict conditions. Portions of a carbohydrate food are fed to a group of volunteers whose blood is then tested at regular intervals, over 2 hours, in order to check blood-glucose levels.

Measuring Glycemic Index of Particular Foods

  • 10 or more volunteers are given a serving of the test-food containing 50 grams of digestible (available) carbohydrate. The actual portion size of each tested food will vary according to how much carbohydrate it contains. The small percentage of carbs in the food, the larger the portion needs to be to provide the standard 50 gram amount of digestible carbs.

  • Example: Carrots contain only about 7 percent carbs, so the portion of carrots eaten by the volunteer will be huge - about 1.5 pounds.

  • Example, Boiled spaghetti contains 25 percent carbs, so the portion of boiled spaghetti eaten by the volunteer will be 200g of spaghetti, which supplies 50g of carbohydrate.

  • To test how the food raises blood-glucose levels, a sample of blood is taken from each subject every 15 minutes during the first hour and thereafter every 30 minutes.

  • The glucose level of these blood samples is then measured and recorded.

  • The glucose level is plotted on a graph and the results are interpreted using a computer program.

  • The volunteer's response to the food being tested is compared with his/her blood-glucose 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.

Glycemic Index Results - How Foods are Classified

Low Glycemic Index Foods
Foods with a GI rating below 55 are considered to have a low glycemic index.

Medium/Intermediate Glycemic Index Foods
Foods with a GI rating between 55 and 70 are considered to have a medium or intermediate glycemic index.

High Glycemic Index Foods
Foods with a GI rating above 70 are considered to have a high glycemic index.

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Carbs-Information.com provides general information about the glycemic index (GI), glycemic load (GL), low GI diets, GI value for all food groups, health problems of high blood glucose including metabolic disorders such as pre-diabetes, impaired glucose tolerance, insulin resistance, hyperinsulinism as well as type 1 and type 2 diabetes. But no information is intended as a substitute for medical advice. Copyright 2003-2018.