Glycaemic Index

Different carbohydrate foods have different effects on blood glucose levels.

The Glycaemic Index (GI) ranks food on a scale from 0-100 according to the effect they have on blood glucose levels. Foods with an index number of 70 or more are considered to be high GI, with an index number between 55-70 as medium GI, and 55 or less as low GI.

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 the Glycaemic Index 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.

However, it is important not to eat large amounts of a food simply because it has a low GI for maintaining blood glucose levels within the ideal range.

What to consider when using the Glycaemic Index for food selection?

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, the fibre and salt content of food are also very important.

Most importantly, you need to watch for fat content of a low GI food. Foods high in fat often have a low GI because fat slows the digestion of food. However, a diet high in fat, especially saturated fat, is not recommended for overweight people or people with diabetes.

Fibre is also frequently found in low GI foods like vegetables, fruits, legumes and many cereals. It adds bulk to a meal without calories, making us feel full as well as slowing the digestive process. These low GI foods are good to include as part of your meal. 

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 it helps slow the digestion and absorption of carbohydrates.

For more information on the Glycaemic Index and GI values please refer to the University of Sydney’s GI website:

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