Glycemic index

Glycemic index (also GI): The glycemic index (GI) ranks carbohydrate-containing foods on a 0–100 scale based on how quickly and how much they raise blood glucose compared to pure glucose (which is 100). It was developed at the University of Toronto in 1981.

How GI is categorized

Low GI (≤55) includes most beans, lentils, whole oats, and most non-starchy vegetables. Medium GI (56–69) includes brown rice, sweet corn, and ripe bananas. High GI (≥70) includes white bread, white rice, and most sugary cereals.

GI vs. glycemic load

GI tells you how fast a food raises glucose, but glycemic load (GL) factors in portion size. Watermelon has a high GI but low GL because a typical serving doesn't have many carbs.

Practical use

GI is useful as a directional tool — favoring lower-GI carbs tends to dampen post-meal glucose spikes. It is less useful as an exact-number tool because GI varies with ripeness, cooking, and the rest of the meal.