Glycymic index

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

The glycaemic index is only a relative measure, however. In addition to this value one must take into consideration how high the carbohydrate content of the given food is. For example, cooked carrots have a much higher GI than raw carrots, but carrots contain only 4 g of carbohydrates per 100 g. Thus, despite their high GI, the cooked carrots will not cause a considerable rise in the blood sugar level.

As mentioned, the GI is important mainly for diabetics. Their blood sugar value improves with a diet that has a relatively low GI, i.e. one abundant in whole-grain products, fruits and vegetables.

For some time now it has been maintained in the press that a low-GI diet will lower the risk of myocardial infarction. In addition, a high GI has recently been connected to the development of overweight. On these points there are only few really secure scientific data, however. On the other hand, it is already clear - and this holds for diabetics as well - that a healthy and preventive diet is not just a matter of the GI, which pertains only to the carbohydrates in food, but also of moderation with fats and choosing the right ones.

Most foods that have a high GI (with at the same time a high carbohydrate content), especially sugar and products rich in sugar as well as white flour and products made with it (white bread, rolls), cannot be classed as particularly valuable from the point of view of nutritional physiology, even independent of their GI. They supply mainly calories, but hardly any essential nutrients. For this reason alone they should be limited in a diet.

In contrast, other foods are valuable and recommended in spite of their relatively high GI. They generally have a low overall carbohydrate content, which means that their higher GI is of considerably less importance. Already mentioned examples are cooked carrots, which one should by no means do without, or melons.