The glycemic index, glycaemic index, or GI is the measurement of glucose (blood sugar) level increase from carbohydrate consumption. Different foods raise glucose to varying levels. The GI estimates how much each gram of available carbohydrate (total carbohydrate minus fiber) in a particular food raises a person's blood glucose level following consumption of the food, relative to consumption of pure glucose. Glucose has a glycemic index of 100, and by definition, other foods have a lower glycemic index.
Glycemic index is defined for each type of food, independent of the amount of food consumed.
A low-GI food will release glucose more slowly and steadily, which leads to more suitable postprandial (after meal) blood glucose readings. A high-GI food causes a more rapid rise in blood glucose levels and is suitable for energy recovery after exercise or for a person experiencing hypoglycemia.
Fruits and vegetables tend to have a low glycemic index. White bread, white rice have a high GI.