What glycemic index measures
Glycemic index, or GI, compares the blood glucose response to carbohydrate-containing foods under standardized testing conditions. It can provide useful context when choosing foods, but it is not a personal glucose forecast or a complete nutrition score. A food’s GI also does not tell you how much carbohydrate is on your plate.
Researchers usually compare portions containing 50 grams of available carbohydrate, meaning carbohydrate that can be digested, with an equivalent amount from a reference food. Blood glucose is measured over two hours. The University of Sydney explains this testing method, which produces an average response across participants.
On the glucose reference scale, GI values of 55 or below are considered low, 56–69 medium, and 70 or above high. These categories describe a food tested in a particular form. They do not mean that every food in the same category has the same nutrients or effect in a mixed meal.
A low GI label therefore answers a narrow question. It does not establish an appropriate serving size, whether a product contains much saturated fat, or whether it meets someone’s overall nutritional needs.
