Glycaemic index (GI)

The glycaemic index (GI) is a measurement of how different carbohydrate foods affect blood glucose levels.

This is especially important for people with diabetes who need to control their blood sugar (glucose) levels. Each type of food we eat has a GI number, and that number tells us what effect that food type has on our blood glucose level. 

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The glycaemic index ranks foods on a scale from 0–100 according to the effect they have on blood glucose. 

  • High GI foods have score of 70 or more on the 0 to 100 scale.  
  • Medium GI foods are between 55 and 70.
  • Low GI foods have a GI score of 55 or less.

Foods with a high GI are those that are quickly broken down into sugars and absorbed into the bloodstream, resulting in a rapid peak in blood glucose levels. This is not good 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.

Some high GI foods are shown in the table below as well suggested alternatives to each.

High GI foods 

Consider swapping for lower GI foods

  • puffed wheat, cornflake, rice flake cereals

  • porridge oats, or bran cereals (with low sugar)

  • sugary soft drinks

  • water, milk or yogurt

  • white bread and some wholemeal breads

  • wholegrain bread and buns

  • white rice or potatoes

  • pasta, noodles (wholegrain even better)

  • chickpeas, kidney beans, lentils

  • watermelon

  • apples, pears, grapes, kiwifruit

If you would like to find out the GI of a particular food, look it up on the database at www.glycemicindex.com

How can a low-GI diet help?

There is now good evidence and research to show that low GI foods/diets help to:

  • Fill you up and keep you satisfied for longer, reducing overeating.
  • Make fat easier to burn and less likely to be stored.
  • Improve cholesterol levels by lowering LDL (bad) cholesterol and raising HDL (good) cholesterol.
  • Manage blood glucose levels.
  • Reduce your risk of developing type 2 diabetes.
  • Reduce your risk of heart disease.
  • Reduce your risk of developing some cancers.
  • Improve mental performance.
  • Sustain energy levels for longer.
  • Improve acne.

Five 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

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 as this has been linked to the development of heart disease. 

Learn more

Glycaemic Index NZ Nutrition Foundation
Visit recipes library Glycaemic Index Foundation
The importance of legumes Diabetes NZ
Top tips to go low GI factsheet  Glycaemic Index Foundation
What you need to know about the glycaemic index Healthy Food Guide

Credits: Diabetes New Zealand. Reviewed By: Julie Carter (NZRD), Community Liaison Dietitian, Auckland DHB