The glycaemic index (GI) is a measure of how quickly and how much blood glucose rises after consuming a food. It was originally introduced to classify carbohydrate-rich foods based on their impact on post-meal blood glucose levels. Low-GI foods are digested and absorbed slowly, leading to a lower and more gradual rise in blood glucose, while high-GI foods cause a rapid increase. Low-GI foods have been associated with reduced risks of certain chronic diseases, such as diabetes and cardiovascular disease. However, the accuracy of GI measurements has been questioned, and alternative methods like the glycaemic glucose equivalent (GGE) have been proposed to better represent food portion sizes. This review discusses methodological considerations for measuring GI, including the number of subjects, test replicates, reference foods, meal volume, and carbohydrate basis. It recommends using at least ten subjects for reliable results, repeating reference food trials at least once, and expressing GI relative to glucose. The choice of reference food is flexible as long as it is calibrated against glucose, and the test meal volume should be standardized to 250 ml of water or 50 g of glucose. The study suggests that the classical GI concept, which focuses on available carbohydrates, may overestimate the impact of low-GI foods due to potential underestimation of indigestible carbohydrates. However, the major determinant of low GI values is often a reduced rate of carbohydrate absorption, rather than malabsorption. The review also highlights the importance of considering second-meal effects, where the metabolic response to a low-GI food can be influenced by the composition of subsequent meals. Overall, the recommendations aim to ensure the quality and reliability of GI measurements, facilitating informed dietary choices and research in this area.The glycaemic index (GI) is a measure of how quickly and how much blood glucose rises after consuming a food. It was originally introduced to classify carbohydrate-rich foods based on their impact on post-meal blood glucose levels. Low-GI foods are digested and absorbed slowly, leading to a lower and more gradual rise in blood glucose, while high-GI foods cause a rapid increase. Low-GI foods have been associated with reduced risks of certain chronic diseases, such as diabetes and cardiovascular disease. However, the accuracy of GI measurements has been questioned, and alternative methods like the glycaemic glucose equivalent (GGE) have been proposed to better represent food portion sizes. This review discusses methodological considerations for measuring GI, including the number of subjects, test replicates, reference foods, meal volume, and carbohydrate basis. It recommends using at least ten subjects for reliable results, repeating reference food trials at least once, and expressing GI relative to glucose. The choice of reference food is flexible as long as it is calibrated against glucose, and the test meal volume should be standardized to 250 ml of water or 50 g of glucose. The study suggests that the classical GI concept, which focuses on available carbohydrates, may overestimate the impact of low-GI foods due to potential underestimation of indigestible carbohydrates. However, the major determinant of low GI values is often a reduced rate of carbohydrate absorption, rather than malabsorption. The review also highlights the importance of considering second-meal effects, where the metabolic response to a low-GI food can be influenced by the composition of subsequent meals. Overall, the recommendations aim to ensure the quality and reliability of GI measurements, facilitating informed dietary choices and research in this area.