Yes that's right and also, processing, the ripeness of a fruit and the variety of a vegetable will also all affect a food’s GI rating. The structure and texture of a carbohydrate have an effect as well. Pasta and durum wheat have a low GI rating, whilst whole grains and high-fibre foods act as a physical barrier that slows down the absorption of carbohydrate. This is not the same as ‘wholemeal’, where, even though the whole of the grain is included, it has been ground up instead of left whole. For example, some mixed grain breads that include wholegrains have a lower GI than either wholemeal or white bread.

There are books that give a long list of GI values for many different foods. This kind of list does have its limitations however. The GI of a food only tells you how quickly or slowly it raises the blood glucose when the food is eaten on its own. In practice, we usually eat foods in combination as meals - bread is usually eaten with butter or margarine, or as an accompaniment to a meal, for example; potatoes are often eaten with meat and vegetables. So cutting out all high GI foods is not the answer. The good thing is you can apply the GI concept so that you can lower the overall GI of a meal by including in it more low GI foods. You need to think about the overall balance of your meals, which should include starchy foods and be low in fat, salt and sugar.
The table below gives an indication of the GI rating for some common foods: