The latest GI values
‘Breakfast is a great opportunity to go for low GI Gold by selecting a low GI breakfast cereal,’ says Prof Jennie Brand-Miller. As there aren’t many low GI packaged breakfast cereals on the supermarket shelves here in Australia, it’s good to see another join the ranks: Kellogg’s Sustain – with a GI of 55 (and that’s on its own, without any milk). Add the milk and fruit and you’ll be well on the way to going for Gold and achieving a lower GI breakfast that Jennie advocates. For more nutrition information check out the Kellogg website: www.kellogg.com.au
My Dutch website gives beer a GI of 110. You say it doesn’t have one. Can you explain the discrepancy?
What you need to know is that a glass of beer has so little carbohydrate that it’s difficult to test its GI. That’s why we listed its GI and GL as 0 in earlier editions of the New Glucose Revolution series books. But eventually we decided that the valid way to test beer (because we are always being asked by beer drinkers) would be by comparing responses to a 10 g carbohydrate portion of beer (about 300 ml or a bit over a cup) with a 10 g carbohydrate portion of glucose (in standard GI testing a 50 g carbohydrate portion is normally used). In this test the GI came out as 66. The GL will be therefore be 66 x 10/100 = 6.6 (round up to 7).
It appears that your Dutch website is quoting a figure from the Montignac database which says maltose beer has a GI of 110. We asked the Montignac people recently (you can contact them through their website) how they determined the GI of foods in their tables. Here’s what they said:
‘We use official published tables when we think they are reliable and make our own calculation with the in vitro method when needed.’
This is clearly of great concern because access to accurate information about GI values is vital for consumers, health professionals and people with diabetes so they can make informed food or beverage choices. The key point is that the GI of a food must be tested physiologically – that is in people not test tubes. There’s a standardised international method of what’s called in vivo (in people) testing adopted by leading labs around the world and Australia has the world’s first published GI Testing Standard (GI News February 2007) which is currently being reviewed by the International Standards Organisation for possible adoption by other member countries. In vitro testing (ie in a test tube) is a handy shortcut method manufacturers sometimes use in developing foods because it’s much, much cheaper to do, but it is also unreliable: it may or may not reflect the true GI of a food. See the discussion about the two different methods in the European Journal of Clinical Nutrition ‘Testing the glycaemic index of foods: in vivo not in vitro’, EJCN (2004) 58, 700–701. Doi:10.1038/sj.ejcn.1601856.
Here’s how the GI is measured in vivo:
To determine a food’s GI rating, 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 (see Figure 1). 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.
If you are unsure about how to use the GI database, just scroll down to the bottom of GI News and see the step-by-step guide.
Where can I get more information on GI testing?
Research Manager, Sydney University Glycemic Index Research Service (SUGiRS)
Human Nutrition Unit, School of Molecular and Microbial Biosciences
NSW 2006 Australia
Phone + 61 2 9351 6018
Fax: + 61 2 9351 6022
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
Where can I get more information on the GI symbol program?