Half an hour after consuming any carbohydrate, the glucose level starts going up, and afterwards it slowly drops until it reaches the initial level; all this happens in approximately two to three hours. This process of glycemic ups and downs called ‘postpandrial response’ depends on the intestines’ pace when absorbing carbohydrates provided by the food during the digestion process.
The glycemic index estimates how much each gram of available carbohydrate in a food raises a person's blood glucose level following consumption of the food.
In this sense, this measurement establishes a classification of all foods, depending on how fast their carbohydrates are absorbed by part of our metabolism. Obviously, glucose is the carbohydrate most rapidly absorbed, and for this reason, it is taken as the unity of measurement with a maximum value of 100.
Dr David Jenkins created this classification in 1981, helping us identify which carbohydrates are healthier for our body.