The glycymic index (GI) was originally developed for the dietary planning of diabetics. It is a measure of the increase in blood sugar following the consumption of foods containing carbohydrates.
As is generally known, our foods contain different kinds of carbohydrates consisting of one, two or very many sugar building blocks. After being digested, the building blocks - mainly glucose - are resorbed into the blood and cause the blood sugar level to rise. With the help of the hormone insulin the sugar is then channelled into the body's cells where it is burnt to produce energy. The various foods containing carbohydrates cause a rise in the blood sugar level with differing speed and intensity.
Their GI is expressed in percent. In order to calculate it, the duration and the elevation of the rise in blood sugar following the consumption of 50 g of carbohydrate from food are measured. This value is then compared with the rise in blood sugar following the intake of 50 g of glucose, which represents 100%.
The GI of a food is determined by many factors. Among others, it depends on how much fibre the food contains. Fibre delays the resorption of carbohydrates and thus lowers the GI. Furthermore, the fat and protein content of the same food is also important. The GI is also influenced by the method of preparation (e.g. raw or cooked), and it changes if the food in question is eaten with other foods in a mixed meal.
Foods without or with only extremely few carbohydrates such as meat, fish, fats and oils have at most an indirect influence on the blood sugar, although it is sometimes maintained that these foods have no GI whatsoever, not even a low one.
The following overview gives examples of foods with a low, medium or high glycaemic index.
Low GI | Medium GI | High GI |
Whole-grain bread, fresh porridge, whole-grain oat flakes, spaghetti and other types of pasta made of durum wheat | Whole-grain crispbread, rice crackers, ready-mixed muesli with sugar added, whole-grain rice | White bread, rolls, baguette, cornflakes, white rice |
- | Potatoes cooked in their skins, boiled potatoes | Fried potatoes, French fries / chips |
Lentils, kidney beans and other legumes, peanuts, almonds, pumpkin seeds | - | - |
Most types of vegetables, raw carrots | Cooked carrots, beetroot, pumpkin / squash, maize / sweet corn | - |
Apples, pears, oranges, peaches, grapes | Pineapple, bananas, melons, raisins | - |
Apple juice, apple juice diluted with mineral water, orange juice, milk | Fruit juice drinks, fruit nectars, beer | Cola drinks, soda pop |
Lactose, fructose, bitter chocolate (more than 70% cocoa) | Marmalade, chocolate, honey, granulated / caster sugar | Dextrose, maltose, corn starch |