The glycaemic index (GI) categorises foods that contain carbohydrates according to their ability to increase blood-sugar levels after intake.


It is measured by comparing the increase of blood-sugar levels after eating a certain type of food that has 50 g of carbohydrates against other foods of reference. The most common foods of reference are glucose and white bread.

The process consists of taking blood samples every few minutes from a person who has just eaten a certain type of food to be later compared with another food of reference. Although it is a long process, its interpretation is very simple: high indexes mean quick absorption, while low indexes mean slower absorption.

Steps to follow:

1. One person eats the necessary quantity of a certain food to achieve the 50 g of carbohydrates. For example: 200 g of cooked noodles.

2. During the next 2 hours, blood samples are taken every 15 minutes.

3. Blood-sugar levels are measured for each sample.

4. A blood-sugar level curve is made in a graph and the under the curve value is calculated using a statistics program.

5. All the curves are compared against the GI of glucose, to which a reference value of 100 is assigned.

GI classification

HIGH GI: equal to or higher than 70 (≥ 70): glucose levels rise quickly and are rapidly absorbed.

MEDIUM GI: between 56 and 69.

LOW GI: equal or lower than 55 (≤ 55): glucose is absorbed more slowly and its levels rise less and more slowly. 

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