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Glycaemic Index Otago

Glycemic Index Otago

Glycemic Index Otago, of the University of Otago, is New Zealand's first accredited Glycemic Index testing laboratory. The protocols used to determine the GI value follows the International Organization for Standardization (ISO 26642:2010(E)) for the determination of the glycemic index (GI) and recommendation for food classification (1) and the Australian Standard for glycemic index of foods (AS 4694-2007) (2). The Glycemic Index Foundation has approved the procedures and testing protocols of Glycemic Index Otago and granted full accreditation (July 2016).

What is the Glycaemic Index (GI)?

The glycemic index (GI) is a scale used to classify carbohydrate-containing foods according to their effect on blood glucose levels. Depending on the rate at which the food is broken down by the body, the food is ranked numerically on a scale of 1 to 100 and classified as low, medium or high GI (Table 1)1. Carbohydrates that break down slowly, releasing glucose at a steady pace into the blood stream, generally have a low GI. The glycemic index is a useful tool to help consumers make informed choices about the right type of carbohydrate for their health and lifestyle.

Table 1. Standard Glycaemic Index Ranking1

Glycemic Index ClassificationGlycemic Index Ranking
Low GI55 or less
Medium GI56-69
High GI70 or more

1 Glycemic Index Foundation. What is the glycemic index?

How is the GI Measured?

The GI of a food is tested in human participants under controlled conditions. Following an overnight fast, healthy individuals consume a portion of a test food that provides 50g (or 25g in some cases) of available carbohydrate. Finger-prick blood samples are taken at baseline, and then again 15, 30, 45, 60, 90 and 120 minutes after consumption. The area under the curve (AUC) is calculated to reflect the total rise in blood glucose levels following consumption. Three glucose references are also measured on separate occasions, and the GI rating (%) of the test food can be calculated by comparing the blood glucose response of the test food to that of the glucose reference. The GI of the test food is reported as the mean ± standard error of the mean (SEM) of the subjects.

The GI is tested in humans under controlled conditions. To determine a food GI rating, measured portions of the test food containing 50 grams (or 25 grams in some cases) of carbohydrate are fed to 12 healthy individuals after an overnight fast. Three glucose references are also measured on separate occasions using the same procedure as described above. Finger-prick blood samples are taken at 15-30 minute intervals over the following two hours. These blood samples are used to construct a blood glucose response curve for the two-hour period. The area under the curve (AUC) is calculated and reflects the total rise in blood glucose levels after eating the test food. The GI rating (%) of the test food is calculated by dividing the AUC for the test food by the mean AUC for the reference food (glucose) and multiplying by 100. The GI of the test food is the mean ± SEM of the 12 subjects.

How Much Does it Cost to Measure the GI of a Food?

Please email us for expression of interest and a current pricing structure. We may offer a 10% discount when testing 6 or more food products. Consideration for a reduction in GI testing costs will be given to existing or previous clients.

Contract Agreement and Confidentiality

Before testing can begin, we require each company to sign a formal contract with the University of Otago to confirm conditions under which GI testing will be carried out, and the ownership and use of data produced. This contract confirms that the testing will be conducted in a confidential manner to protect the company's commercial interests. In addition, the payment details and timeline of the research will be specified.

How Much Product is Needed to Test Glycemic Index?

To determine how much product is needed for GI testing, we need to know the carbohydrate content of the product. A chemcial analysis of the food product for direct determination of available carbohydrate and/or available carbohydrate by difference through an appropriate laboratory. Please contact us for details regarding this.

How Long Does it Take to Test a Product?

After a signed contract has been received, particiapnts are recruited and the portion size of the test food is calculated based on the results from the chemical analysis. It then takes between 10 and 15 working days to complete testing, depending on the number of food products being tested. As blood samples are collected, we need to allow time for study participants to recover between each testing day. Once all testing has been completed, a full report including the mean GI value for the test food(s) is produced and will be emailed to you.

I want to use the GI Symbol on my product packaging?

As an accredited Glycemic Index testing laboratory, we meet all of the necessary requirements for the testing of products which intend to use the GI symbol. Please note however, that there are other requirements outside of our testing processes that may need to be met. We advise you contact the Glycemic Index Foundation to obtain further information.

Contact Details

Dr Tracy PerryGlycemic Index Otago
Email: of Human Nutrition
Phone: +64 3 479 7508University of Otago
PO Box 56
Tel 64 3 479 5430
Fax 64 3 479 7958