Firstly, the index to what? Originally, one gave glucose a score of 100 as the fastest-releasing of all sugars. Another used white bread, meaning glucose would score over 100 in that index. But now, everyone has agreed to use glucose as the index.

Secondly, the effect measured is the effect produced by feeding people the amount of any given food required to give 50g of carbohydrate. Here lies a more significant problem. That' s a lot of carrots (which are largely water) or a very tiny amount of, say, chocolate. This tends to create the impression that fruits and egetables have a high GI score and hence should be avoided when, in truth, the amount we eat would not have a pronounced effect on blood sugar.

There would be some merit in giving the GI for a serving of a food, rather than the amount required to achieve 50g. This is becoming more popular and is sometimes called the ' glycaemic load' of a food. I have done this in some instances in the charts in my books to give a more publicly realistic view. It is also worth pointing out that not all researchers (hence individuals) respond in the same way, so a GI for afood is an average response, usually of a relatively small number of people.