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What is the glycaemic index and why is it so important?

Written by Kevin, Nutritionist (M.Sc. Medical Science)

Not all foods have the same effect on blood sugar and insulin levels. Whether your blood sugar levels rise quickly, moderately or slowly after a meal depends largely on the glycaemic index (GI) of the food you consume.

The GI is a ranking of how quickly each carbohydrate-containing food or drink makes blood glucose rise after eating them. However, different carbohydrates are digested and absorbed at varied rates. The GI index runs from 0-100 and usually uses glucoses, which has a GI of 100 as reference. The lower the GI, the slower and more gradual the rise in blood sugar levels.

Meat, fish and low-fat dairy products are a good choice. Vegetables, pulses and wholegrain products also have a low GI thanks to the complex carbohydrates they contain. Complex carbohydrates are processed by the body more slowly and cause blood sugar to rise less rapidly than simple carbohydrates which pass quickly into the bloodstream. The GI of fruit varies greatly. For example, the GI of berries, apples and cherries is lower than watermelon or pineapple. Generally speaking, foods with a GI of less than 55 are better choices as these are deemed ‘low’. Foods with a GI over 70 are categorised as ‘high’ and should be avoided as much as possible.

The GI is particularly important for people with Type 2 diabetes and those who wish to lose weight. Foods with low GI also increase the feeling of fullness. They are slowly absorbed into the body and ensure blood sugar levels are only raised slightly while the body's requirement for insulin is reduced. As a result of this lower insulin requirement, fat stores are utilised for energy thereby making it easier for those with Type 2 diabetes to lose weight.

The effects of meals with differing GI’s can be clearly seen by checking your own blood sugar. If you measure your blood sugar 1 to 1.5 hours after eating food with a low GI, you will see a smaller increase than if you make a comparable measurement when you have eaten foods with a high GI.

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