Glycaemic Index and Diabetes

What is the glycaemic index?

The glycaemic index (GI) is a number from 0 to 100 that tells us the rate at which a food raises blood glucose levels. This makes it extremely useful for people with diabetes to understand GI rating for different foods.

Different carbohydrates are absorbed by the body at different rates and knowledge of this can enhance blood glucose control. There will be different times when different food rating GI rating are suitable for consumption. E.g. when blood glucose is low you will benefit from high GI foods for a quick spike in blood glucose levels.

The GI ratings vary from 0-100, with 100 based on pure glucose. The lower the rating, the slower the carbohydrate is absorbed (which means less spikes in blood glucose levels). This graph demonstrates clearly the difference in blood glucose levels when comparing low GI food and high GI food consumption.

*This graph is designed to give a general overview of different GI Index foods. This is designed to increase your knowledge on food GI ratings and should not be used to dictate medical care.

GI ratings have been put into 3 categories in the graph, here we will show how these categories are distinguished:

Low GI: Under 55 rating

Med GI: 55-70 rating

High GI: Over 70 rating


Different foods and GI rating categories:

Low GI

Baked Beans

Kidney Beans


Fruit loaf


Medium GI




Bran flakes

Cous Cous

Muesli Bar

High GI

Sports drinks

Jelly babies

Jaffa cakes





You may now be thinking that is makes sense to have a diet of mainly low GI foods and blood sugars will remain stable. Unfortunately, there are many other factors to consider.

Firstly, not all low GI foods are healthy choices. For example, foods with high fat content may have a low GI rating because the fat slows down the absorption of the carbohydrates. Secondly, food may have a low GI rating but be high in carbohydrates. The amount of carbohydrates you eat will have a bigger impact on blood glucose levels than GI alone.


There are other factors which determine the GI level of foods, these are:

Ripeness of certain fruit and vegetables.

Method of cooking.

Wholegrain and high fibre foods will slow down the absorption on carbohydrates.

Higher protein levels lower the GI rating in foods.

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