GI Update

GI Q&A with Prof Jennie Brand-Miller


‘I have seen numerous studies stating that chewing food completely (20–30 times) is beneficial in suppressing appetite. However, if we chew an apple before swallowing, is the GI value that of an apple or of apple juice?’ – Norm
Hi Norm, the GI of a food (or beverage) is based on scientific testing of real foods in real people in the state in which they are normally consumed – so when testing, an apple is crunched and chewed in the normal way and the subsequent GI value is for a chewed and digested apple – skin and all. If you chewed the apple over and over again in the mouth until it’s a very soft mash, then chances are the glucose and insulin response will be higher. We know what happens if we chew bread and pasta for longer before swallowing. This produces a higher glucose response because saliva contains the enzyme amylase that begins the process of starch digestion. In fact, these studies showed that a minute or two of chewing caused over half the starch in bread to be digested before it was swallowed. The pasta, however, was more resistant to digestion in the mouth, partly because of its hard texture.

Here’s how scientists measure a food’s GI value (you’ll find lots more information on our website: ‘To determine a food’s GI value, measured portions of the food containing 10–50 grams of carbohydrate are fed to 10 healthy people after an overnight fast. Finger-prick blood samples are taken at 15–30 minute intervals over the next two hours. These blood samples are used to construct a blood sugar response curve for the two hour period. The area under the curve (AUC) is calculated to reflect the total rise in blood glucose levels after eating the test food. The GI rating (%) is calculated by dividing the AUC for the test food by the AUC for the reference food (same amount of glucose) and multiplying by 100. The use of a standard food is essential for reducing the confounding influence of differences in the physical characteristics of the subjects. The average of the GI ratings from all ten subjects is published as the GI of that food.’

GI graph

GI testing by an accredited laboratory

North America

Dr Alexandra Jenkins
Glycemic Index Laboratories
36 Lombard Street, Suite 100
Toronto, Ontario M5C 2X3 Canada
Phone +1 416 861 0506

Fiona Atkinson


Research Manager, Sydney University Glycemic Index Research Service (SUGiRS)
Human Nutrition Unit, School of Molecular and Microbial Biosciences
Sydney University
NSW 2006 Australia
Phone + 61 2 9351 6018
Fax: + 61 2 9351 6022

New Zealand
Dr Tracy Perry
The Glycemic Research Group, Dept of Human Nutrition
University of Otago
PO Box 56 Dunedin New Zealand
Phone +64 3 479 7508

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