Measuring the GI
 Measuring the glycemic index or GI rating of a food is conducted under strict conditions, although sampling methods can vary slightly.
Typically, 10 or more volunteers are given a serving of the test-food containing 50 grams of digestible carbohydrate. The actual portion or serving size of each tested food varies according to how much carbohydrate it contains, based on official food composition tables.
The smaller the percentage of carbs in the food, the larger the portion needs to be in order to provide the standard 50 gram amount of digestible carbs. Thus in practice, if a food contains a very small proportion of carbohydrate, necessitating a very large test serving size, the test serving is typically scaled down.
A sample of blood is then taken from each subject every 15 minutes during the first hour and thereafter every 30 minutes. These blood samples are laboratory-tested for glucose content and the results recorded.
The glucose level is plotted on a graph and the results are interpreted using a computer program.
The volunteer will provide a blood-glucose reaction to the food by being tested in comparison with his or her response to 50g of pure glucose. These comparative tests using pure glucose are typically conducted several times, on several occasions, to provide a mean response.
The average blood sugar response from 8 to10 volunteers determines the GI value of that food.
GI Rating Categories:
Low GI Food
These are foods with a GI rating below 55.
Intermediate or Medium GI Food
These are foods with a GI rating between 55 and 70
High GI Food
These are foods with a GI rating above 70
Best Low GI Diets
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