The glycaemic index (GI) of a food indicates how much effect it has on blood glucose. Values range from 0 (no effect) to 100 (large effect). Foods that contain no carbohydrate have a GI of 0, e.g. meats, fish and eggs. Cheeses generally have a very low GI and glucose has a GI of 100. However, GI is a very complex subject. Different methods of food processing or preparation can have a large effect on the GI of a food. The ripeness of certain foods can also have a large effect on their GI. For example, when bananas have been stored for a few days and become riper, much of the starch turns to sugar and the GI increases. Also, different strains of rice have different GI values.

• Low GI Foods: eg. peanuts, milk, yogurt, apples, pears, kiwi fruit, orange juice.
• Medium GI Foods: eg. boiled potatoes, cheese & tomato pizza, wholemeal bread, Weetabix.
• High GI Foods: eg. white bread, Coco Pops, Cornflakes, white rice, french fries.

Click here for more information on the GI values of foods.

The GI of a meal will depend not only upon the GI of each food which will be variable as discussed above, but also upon the specific food combinations and how the meal is prepared. In addition, the GI of a particular meal may be influenced by what was eaten in the previous meal. See Flint et al (2004) for further information.

The glycaemic load (GL) of a food needs to be considered as well as the GI.

For example, a serving of pasta has a higher GL than a slice of white bread and thus has a greater effect on blood glucose level.

Choosing foods with a low GL may help those with diabetes to build a healthy diet. It is not clear whether this might also be helpful to the general population, although a diet containing wholegrain cereals may have a number of health benefits.

Calculating Dietary GI and GL

You can calculate both dietary GI and GL using Tinuviel Software Products:

• WISP - weighed food intake records or food diaries. Click here for details.
• QBuilder - food intake questionnaires. Click here for details.

Background on the GI/GL calculations can be found in the Technical Archive.

References

Aston LM et al. Determination of the glycaemic index of various staple carbohydrate-rich foods in the UK diet. Eur J Clin Nutr 2008;62:279–285.

Flint A et al. The use of glycaemic index tables to predict glycaemic index of composite breakfast meals. B J Nutr 2004;91:979-989.