Headington Campus - Oxford Brookes University

Why choose Brookes?

OxBCNH is internationally renowned for its work on glycaemic index (GI) and we have published extensively in this area. The OxBCNH is the only GI testing centre in Europe accredited by the Glycemic Index Foundation. Our procedure for GI testing is carried out in accordance with ISO 26642:2010 standards (ISO 26642:2010 Food Products – Determination of Glycaemic Index).

Logo of Oxford Brookes Centre for Nutrition and Health

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). 

Glycemic Index graph

How is GI measured?

Researcher reading the breath hydrogen result for a participant.

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, a control of three glucose references are measured on three different occasions.

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 minutes for the first hour and then every 30 minutes for the next two hours
A participant eating a sample of food in the kitchen of the Oxford Brookes Centre for Nutrition and Health.
Researcher working at a computer in the office of the Oxford Brookes Centre for Nutrition and Health.

From the result obtained from stage two, the area under the curve (AUC) is calculated. This reflects the total rise in blood glucose levels after eating the test food or drink. The final GI value of a food is the average for all participants.

The GI of the food is calculated:

Glycemic Index equation