What is the Glycemic Index? - the glycemic index explained

About glycemic index – the glycemic index explained

What is the glycemic index?

The glycemic index, or GI for short, was formulated by Dr David J Jenkins and his colleagues in the early 1980s at the University of Toronto. It is a scale which measures how much carbohydrate-rich foods raise blood glucose levels, in relation to glucose or white bread.

When we eat foods with carbohydrates, they are broken down during digestion and converted to glucose (sugar). Our bodies then use the glucose for energy, to fuel various processes.

Thus, after eating, our blood glucose levels rise. How quickly the foods we eat raise our blood glucose levels is termed the ‘glycemic response’.


What is glycemic index?

When we fix the amount of available carbohydrates eaten, and then compare the impact of a food on blood glucose levels to the impact on blood sugar levels of the same amount of a base food, usually glucose but sometimes also white bread, then we arrive at a particular figure, termed the ‘glycemic index’.

If the carbohydrates in a certain food break down quickly during digestion, thus releasing glucose at a relatively faster rate into the bloodstream, the food is considered to have a high GI.

Conversely, if the carbohydrates in another food break down slowly during digestion, thus releasing glucose at a relatively slower rate into the bloodstream, then the food would be considered to have low GI.

The rate of release of glucose into our bloodstreams has a direct impact on the rate of fluctuation of insulin levels in our bodies.

Do note that foods with little or no carbohydrates in them do not typically have a glycemic index value.


What is the glycemic index affected by?

There are a few factors which determine glycemic response, including the amount of food eaten, the degree of food processing carried out, as well as the method of food preparation and cooking.

A few factors usually influence the glycemic index value of a certain food, among them the amount of fiber in the food; the type of starch which is contained in the food; how the starch molecules are physically contained with the food; and the amount of fat and protein in the food.


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.


Importance of the glycemic index – how and what is the glycemic index impact on health?

Besides the fact that they do not cause drastic spikes in one’s blood glucose levels, low-GI foods are usually also healthier options, providing more nutrient and fiber content, while having lower levels of fats and calories.

Thus, overall, low-GI foods are taken to be healthier food options, and many people plan their diets with the glycemic index firmly in mind.

I hope this page has given you an overall idea of what is a glycemic index value and how the glycemic index works.

For more information on the health benefits of low glycemic diets and low glycemic food, and the corresponding detrimental effects of high glycemic foods, click here.



Glycemic Index-related Pages

What is the Glycemic Index? - the glycemic index explained | Benefits of Low Glycemic Diets and Low Glycemic Food | Glycemic Index of Foods - limitations of the value | Eating Low Glycemic Foods - some tips | Glycemic Index Listing of Foods | Low Glycemic Food List | High Glycemic Foods to Avoid or Cut Down on