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Glycaemic testing

What is GI?

The glycaemic index (GI) is a method of ranking foods on a scale of 1 to 100 according to the extent to which a food raises blood sugar levels after ingestion. The principle is that the slower the rate of carbohydrate absorption, the lower the rise of blood glucose level and the lower the GI value. A GI value ≥70 is considered high, a GI value 56-69 (inclusive) is medium and a GI value ≤55 is low (where the glucose standard = 100).

How is GI measured?

Our GI tests involve a minimum of 10 healthy human participants, who are required to fast at least 12 hours before their test session. Prior to GI testing of a food, three glucose references are measured on three different occasions (50g or 25g of available carbohydrate portions, depending on the test food).

On the day of testing

Two fasted capillary blood samples are taken by trained personnel
The test food / glucose drink is consumed within 15 minutes
Capillary blood samples are taken every 15-30-minute intervals after consumption for two to three hours.

From this, the area of the curve (AUC) is calculated that reflects the total rise in blood glucose levels after eating the test food or glucose drink. The final GI value of a food is the average of all participants.

The GI of the food is calculated:

FAQs

What is available carbohydrate?

Available carbohydrate is the portion of a carbohydrate that can be digested by human enzymes and absorbed by the small intestine. Available carbohydrates are glycaemic and provide carbohydrate for metabolism and energy. According to the FAO, available carbohydrate is defined as “starch and soluble sugars”.

What is the OxBCNH testing process?

Once the client contract is signed, participant recruitment begins. Participants are screened before starting every new study. We do a minimum of two reference glucose tests on each participant. Reference glucose tests and participant demographics are updated every 3 months. Blood glucose measurements are taken by trained research assistants every 15 mins for the first hour post food/drink consumption and every 30 mins for the second and third hour. The glycaemic index is calculated with data checked by the RAs and PI on the study. The report is written by the RA and PI and checked by the centre manager. The length of the testing process is unique for each study, the minimum time required to complete a GI study is 4 weeks.

What foods can be tested?

Here at OxBCNH, we test a wide variety of food, drinks and meal supplements. Previously tested products include breakfast cereals, meal supplement drinks, fruit juices and honey/sweeteners. The best way to check that we can test your product is to contact our centre manager, by emailing oxbcnh@brookes.ac.uk.

What information do I need to provide to begin testing?

In order to begin testing, the client and OxBCNH must both sign a unique contract, detailing start and finish dates, number of participants, type of product and the testing that is being carried out. You may need to provide the ingredient and nutritional information of the product.

What happens once testing is complete?

Once the report is complete, the centre manager will send on the final version to the client. A subsequent virtual meeting can be arranged to address any further queries that clients may have. We ask that clients fill out our feedback form once testing is complete as we are always eager to get feedback and improve our services.

Can our results be published?

If you are interested in publishing results of your study, it is best to contact our centre manager or the principal investigator to get expert advice on how to go about it.

What is the Glycemic Index Foundation?

The Glycemic Index Foundation is a non-profit health promotion charity that primarily provides the community with tools and information about GI. The GI Foundation’s main vision is to present the public with the nutrition and health benefits of including low GI products in the diet. There are many user friendly resources on the Glycemic Index Foundation website.

What are the ISO guidelines?

The International Organization for Standardization (ISO) is a worldwide federation of national standards bodies. ISO standards are internationally agreed by experts in the specific area. For GI testing, OxBCNH follows ISO 26642:2010 standards. These standards were developed to standardize the method of determining GI of foods for practice and research purposes. Find out more.

Glycaemic testing