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Another great thing to think about is portion size – because the total amount of insulin your body produces depends not just on a food’s GI but also on its carbohydrate density – also known as the glycaemic load.

The GI only reflects how quickly a food raises blood sugar levels – it doesn’t take into account how much of that food makes up an average portion. And the amount of carbs in an average portion is what actually goes into your body on a day-to-day basis – so this is what the GL measures: the glycaemic effect of an average portion of a food. The GL of a food is obtained by dividing the GI value by 100, then multiplying by the amount of total carbohydrate per typical serving of the food.

A low-GL food is considered 10 or less, medium 11–19 and high would be 20 or more.

The great thing about this is that a food that can come up high on the GI table might actually come out low on the GL, because you wouldn’t eat enough of it in an average portion to send your blood sugar soaring.

For example, carrots have a glycaemic index value of 92 which is high. But, in a typical serving size of one-half cup, there’s only 4.2 grams of carbohydrate. So, the calculated GL is only 3.9, which is very low, showing that this food is unlikely to cause a disturbance in blood sugar or insulin response. By contrast, a plain bagel provides 65 grams of carbohydrate and has a GI of 73. Its glycaemic load is therefore a massive 47.

The following chart will help you identify both the GI and GL of commonly eaten foods.