Explaining The Glycemic Index And Glycemic Load Of Foods

What is the Glycemic Index? – understanding the glycemic index and how glycemic index is measured

After the consumption of a fixed amount of carbohydrates from a certain food (say, Food-X), usually 50g, we then plot a graph of the change in blood glucose levels (Y-axis) against time (X-axis) for a period of 2 hours. The area under the curve is then obtained.

Separately, a similar graph is plotted for a base / reference / standard food, usually glucose but sometimes also white bread, and the area under that curve also obtained.
The first area, for Food-X, is then divided by the second area for the reference food, and multiplied by 100 – this then gives us a figure, which is commonly known as what is the glycemic index.

What is the glycemic index base / reference / standard food usually used?

When glucose is used as the standard or reference food, its glycemic index is, by definition, 100.

When white bread is used as the standard or reference food, the glycemic index of measured foods would then be different. With glucose as the base food, the GI of white bread is about 71.

The main advantage of using glucose as the reference food is that it is a fairly universal food item. The measured GIs of other foods can thus be easily compared across the board. Another advantage is that the maximum end of the GI scale would terminate near the 100-mark, thus enabling one to have a better sense of the degree of glycemic response for a certain food.

On the other hand, when white bread is used as the reference food, it is difficult to compare foods using a standard scale, since there may be more variation in the type of white bread used for testing. The GI scale would also stretch way beyond the 100-mark.

The good thing, however, is that people would have a real food with which to compare other foods with. For example, someone would be able to compare wholemeal bread with white bread and get a rough sense of the glycemic response of the former; people do not really eat glucose as a standalone food and thus its uses in this regard would be limited.

What is the glycemic index range for low, mid-range and high GI?

With glucose used as the standard or reference food, the commonly used range for low GI is less than 56, mid-range GI from 56 to 69, and high GI at 70 or more.

Generally speaking, the lower the GI value of a food, the better the quality of carbohydrates which it contains.

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