The glycaemic index (GI) is a measure of how quickly and how much a food raises blood glucose levels after consumption. It was originally developed to classify carbohydrate-rich foods based on their impact on postprandial blood glucose. Foods with a low GI are digested and absorbed slowly, leading to a gradual rise in blood glucose, while high-GI foods are rapidly digested and absorbed, causing a sharp increase. Low-GI foods have been associated with benefits for certain chronic diseases, such as cardiovascular disease and diabetes. However, the measurement of GI requires standardized methods to ensure consistency and accuracy. The GI is calculated based on the area under the curve (AUC) of the blood glucose response to a 50 g available carbohydrate (CHO) test dose, compared to a reference food (usually glucose). The number of subjects, their characteristics, and the conditions under which the test is conducted are critical factors that influence the reliability of GI measurements. Typically, at least 10 subjects are recommended to ensure sufficient statistical power and precision. The reference food should be standardized and calibrated against glucose to ensure consistency across studies. The test food should be consumed within a reasonable time frame to minimize gastric emptying effects and ensure accurate measurement of blood glucose responses. The volume and composition of the test meal can also influence the glycaemic response, so it is important to standardize these factors. For solid meals, consumption should be completed within 10–15 minutes, while for liquids, it should be within 5–10 minutes. Blood samples should be taken at regular intervals, with the first sample taken 15 minutes after the first bite or sip. The concept of GI is based on available CHO, which is defined as total CHO minus dietary fibre. However, this approach has been criticized for potentially overestimating the amount of available CHO in foods, especially those containing indigestible carbohydrates. Alternative methods, such as glycaemic glucose equivalent (GGE) and glycaemic load (GL), have been proposed to provide a more comprehensive understanding of the glycaemic impact of foods. These methods consider both the amount and type of carbohydrates in a food, as well as other dietary components. The measurement of GI requires careful consideration of various methodological factors, including the number of subjects, the reference food, the test dose, and the conditions under which the test is conducted. Standardized procedures are essential to ensure the accuracy and reliability of GI measurements, which in turn support the use of GI as a tool for making healthier food choices.The glycaemic index (GI) is a measure of how quickly and how much a food raises blood glucose levels after consumption. It was originally developed to classify carbohydrate-rich foods based on their impact on postprandial blood glucose. Foods with a low GI are digested and absorbed slowly, leading to a gradual rise in blood glucose, while high-GI foods are rapidly digested and absorbed, causing a sharp increase. Low-GI foods have been associated with benefits for certain chronic diseases, such as cardiovascular disease and diabetes. However, the measurement of GI requires standardized methods to ensure consistency and accuracy. The GI is calculated based on the area under the curve (AUC) of the blood glucose response to a 50 g available carbohydrate (CHO) test dose, compared to a reference food (usually glucose). The number of subjects, their characteristics, and the conditions under which the test is conducted are critical factors that influence the reliability of GI measurements. Typically, at least 10 subjects are recommended to ensure sufficient statistical power and precision. The reference food should be standardized and calibrated against glucose to ensure consistency across studies. The test food should be consumed within a reasonable time frame to minimize gastric emptying effects and ensure accurate measurement of blood glucose responses. The volume and composition of the test meal can also influence the glycaemic response, so it is important to standardize these factors. For solid meals, consumption should be completed within 10–15 minutes, while for liquids, it should be within 5–10 minutes. Blood samples should be taken at regular intervals, with the first sample taken 15 minutes after the first bite or sip. The concept of GI is based on available CHO, which is defined as total CHO minus dietary fibre. However, this approach has been criticized for potentially overestimating the amount of available CHO in foods, especially those containing indigestible carbohydrates. Alternative methods, such as glycaemic glucose equivalent (GGE) and glycaemic load (GL), have been proposed to provide a more comprehensive understanding of the glycaemic impact of foods. These methods consider both the amount and type of carbohydrates in a food, as well as other dietary components. The measurement of GI requires careful consideration of various methodological factors, including the number of subjects, the reference food, the test dose, and the conditions under which the test is conducted. Standardized procedures are essential to ensure the accuracy and reliability of GI measurements, which in turn support the use of GI as a tool for making healthier food choices.