Glucose raises blood sugar quickly and is assigned the value of 100. Other foods, depending on whether they raise blood sugar slowly or rapidly are given a number on the 0-100 scale. Carbohydrates that release glucose rapidly into the bloodstream have a high GI – 70 and above, carbohydrates that release glucose moderately into the bloodstream have a medium GI – 56-69 and carbohydrates that release glucose more gradually into the bloodstream have a low GI – below 55.
| Classification | GI range | Examples |
| Low GI | 55 or less | Most fruit and vegetables, legumes / pulses, nuts and seeds, milk, yogurt. |
| Medium GI | 56–69 | Whole wheat products, basmati rice, sweet potato, table sugar. |
| High GI | 70 and above | Corn flakes, rice krispies, (Most breakfast cereals) baked potatoes, watermelon, croissants, white bread, white rice. |
There are some criticism of the GI – that we may eat way more than 50g of carbohydrate from a certain food such as pasta of rice that may be classified as medium GI, and way less than 50g of carbohydrate from another medium or high GI foods such as watermelon (watermelon is mainly water!).