What is the Glycaemic Index (GI)?

The Glycaemic Index (GI) is a relatively new concept in nutrition that looks at how different carbohydrate foods affect blood glucose levels. The Glycaemic Index ranks foods on a scale from 0-100 according to the effect they have on blood glucose. Foods with an index number of 70 or more are considered to be high GI; foods between 55 and 70 as medium GI; and foods of 55 or less as low GI.

High GI causes rapid peaks

Foods with a high GI are those that are rapidly digested and absorbed, resulting in a rapid peak in blood glucose levels. This is not ideal for people with diabetes, who try to keep their blood glucose levels fairly stable, without rapid changes in level (peaks or troughs). By contrast, low-GI foods, provided they are also low in fat, are best for controlling diabetes. This is because they produce a gradual rise in blood glucose and insulin levels because of their slow digestion, absorption and gradual release of glucose into the bloodstream. This avoids rapid peaks and troughs.

How can a low-GI diet help people with diabetes?

There is evidence that a low-GI diet can help control established diabetes, help people to lose weight and lower blood lipids (fats), and improve the body’s sensitivity to insulin by keeping blood glucose levels more stable than when high-GI foods are consumed.

How do I use the GI?

It’s important to remember that the GI alone should not be your only criteria when selecting what to eat. The total amount of carbohydrate, the amount and type of fat, and the fibre and salt content of food are also very important.

Most importantly, you need to watch for fat content as well as the GI. This is because foods high in fat often have a low GI (fat has been shown to slow digestion). However, a high-fat diet is not recommended for overweight people or people with diabetes. [High-fat diets, especially high saturated-fat diets, are also not recommended for the general population in the long term, as this has been linked to the development of heart disease. Also see: Heart risk factors - eating and nutrition]

5 simple ways to change to a low-GI diet

1. Include one low-GI food at each meal.
2. Switch to breakfast cereals based on barley, oats (such as porridge), wheat and rice bran.
3. Eat grainy breads made with whole seeds, barley and oats, and pumpernickel instead of white or brown bread.
4. Eat pulses and legumes (such as beans, lentils and peas).
5. Eat high-fibre foods because fibre helps slow the digestion and absorption of carbohydrates.

More about the GI

For more information on the Glycaemic Index and GI values see the University of Sydney's GI website www.glycemicindex.com or consult with your local dietitian.

Original material supplied by Diabetes New Zealand, 2008. Edited by everybody, August 2011.