The Glycaemic Index – Explained

What is the Glycaemic Index and why is it important to my health?

The Glycaemic Index (GI) helps us to understand the difference between carbohydrates (or carbohydrate containing meals/snacks) when they enter our bodies. The GI ranks foods from 0-100 depending on their effect on our blood sugar levels.


First a few basic principles: Every time we eat carbohydrate it is broken down in our gut into glucose (or simple sugar). This sugar is then transported around the body in our blood stream and taken up by cells to be used as energy. Insulin is a hormone that tells body cells to take up sugar from the blood stream.


What is the difference between HIGH and LOW GI foods?

High GI foods (GI>69) are rapidly digested by the gut and absorbed into the blood stream causing a rapid rise in blood sugar levels. Our body’s response to these high sugar levels is to release insulin in large quantities to quickly bring sugar levels back down below potentially harmful levels. This rapid drop in blood sugar levels is felt as a drop in energy levels (see graph opposite). Some people describe it as feeling lethargic, anxious and struggling to concentrate about 1 hour after eating a high GI snack or meal.

Examples of high GI foods: soft drink, lollies, cakes, sweet biscuits, white flour, white bread, rice bubbles, corn flakes, white bread sandwich with little protein or vegetable filling, jasmine rice


nutrition_giLow GI foods (GI< 55) are digested at a much slower rate in the gut. Therefore sugar enters the blood stream more gradually and blood sugar levels stay within a lower and healthier range.  This means that the hormone insulin is released in smaller quantities and as a result our blood sugar levels are maintained relatively stable between meals. As such the benefits of consuming low GI foods include: preventing rapid fluctuations in energy levels, reducing food cravings; feeling fuller for longer; improving endurance during physical activity; weight control; prevention and management of chronic diseases (diabetes, insulin resistance and cardiovascular disease).

Examples of low GI foods: wholegrain breads (such as Burgen), wholemeal sourdough bread, wholegrain cereals (such as All Bran, rolled oats, muesli, Guardian), pasta, noodles (soba/Hokkein/Udon), barley, basmati rice, quinoa, sweet potato, legumes, most fresh fruits, dairy (yogurt,  milk,).

(note: Only foods that contain carbohyrate can be ranked using the GI. Foods made of protein and fat only, such as meats, cannot be given a GI ranking. Non-starchy vegetables are very low GI or have no GI as they contain no carbohydrate, however they are full of fibre so adding them to a dish will make it lower GI. As a simple rule adding protein and fibre to a dish is an excellent way to make it lower GI).


Insulin – Fat Burning and Weight Management:

It is important to note that when levels of the hormone insulin are high (such as after eating high GI foods) we are not going to burn fat. Insulin is an anabolic hormone and sends signals to the body to tell it that there is “plenty of sugar around” and to “stop fat burning.” So a diet based primarily around high GI foods can have a double whammy effect of leaving us feeling hungry and tired all the time but also be preventing us loosing fat!

For more information on choosing low GI go to the Go Grains website:

Christa Payne

Dietitian APD, AN / Exercise Scientist

Author: Eat Me Nutrition

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