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By Dr. Keith E. Lewis
June 25, 2008


The glycemic index of foods is a ranking system. It is a ranking system of foods according to their impact on blood glucose levels. All foods are compared to a reference food. That reference food is pure glucose. The glycemic index ranking method rates foods on a scale of 0 to 100 with a glucose being 100. The glycemic index gives us critical information about the type of carbohydrate we are consuming in our diets. The glycemic index is a clinically proven tool in its application not only to diabetes, but also weight control and cardiac health. Unfortunately we cannot measure the glycemic index of foods based solely on the foods composition. To test the glycemic index, you need real people with real food.

What is the testing process and how does it work?

Scientists measure the glycemic index by measuring the amount of food containing a standard amount of carbohydrate. This carbohydrate is given to a volunteer to eat. Over the next 2 hours and in diabetics 3 hours, blood samples are taken ever 15 minutes during the first hour and thereafter every 30 minutes. The blood glucose level of the blood sample is measured in the laboratory and recorded. Blood glucose levels are plotted on a graph and using computer models the effect on blood glucose is measured. As foods are tested for the glycemic index or GI, the average GI is found in a sampling of 8 to 10 or 12 different individuals and based on averages, the GI value is determined. Once glycemic index values are determined, the foods are then categorized based on the following:

    1. High glycemic index - 70 or higher
    2. Intermediate glycemic index - 56 to 69
    3. Lower glycedmic index - 0 to 55

The higher the glycemic index value, the higher the blood glucose levels after consumption of food. Foods with a high GI value usually reach a higher peak or a higher glycemic spike much quickedr, but sometimes with some foods, glucose levels remain high for the whole 2-hour period of testing. White bread is a good example of this.

 A slow digestion and gradual rise and fall in blood glucose responses after eating low GI food helps to control blood glucose levels in  people with diabetes or glucose intolerance and of course, the benefits of following a program such as the GI helps healthy people as well because it does reduce the secretion of the hormone insulin over the course of the day resulting in fewer insulin spikes.

Slower digestion also helps delay the feeling of being hungry and obviously can also help promote weight loss in overweight people.

 Lower blood blucose levels over the course of the day also reduce the inflammatory load experienced by our bodies, espeically noted inflammation of the blood vessels in heart, so consequently coronary health is improved, oxidative stresses are reduced, and we can control better glycemic spikes, so in summary the glycemic index is a measure of the effect of a food, particularly a carbohydrate, on blood glucose levels.

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