GI Values Update

New GI values
How true is the low GI blue tortilla story?
We recently received a ‘EurekAlert’ press release that stated that ‘people with dieting blues should try swapping white corn tortillas for blue which had ‘less starch and a lower glycaemic index than their white counterparts.’ Along with ‘20% more protein.’ The study was reported in the Journal of Science of Food and Agriculture (DOI 10.1002/jsfa.3008). The authors state in the press release that ‘one important benefit of the lower GI blue tortillas is their potential role in preventing or controlling metabolic syndrome … stroke and diabetes.’ The findings received a whole heap of publicity (enough to make us pretty envious) and sounded like just the thing for our GI News readers so we thought we should check the story out. Sadly, we have to set the record straight.

Blue tortillas may indeed have a lower GI than white, but it hasn’t actually been tested in people following the international standardised method. It’s just been guesstimated. What the researchers actually did was compare the tortillas ‘with respect to in vitro starch digestibility – available starch, total and retrograde resistant starch contents, amylolysis rate’ and then predict the GI. So we actually don’t know the GI at all.

But we do know that Mexican corn tortillas (white ones) prepared the traditional way using nixtamalized (see below) maize grains have a low GI because they were tested some years ago, the results were published in a peer -reviewed journal (Noriega E, Rivera L, Peralta E. Diabetes Nutr Metab 2000; 13: 13-9.) and are already on the GI database.

Mexican corn tortilla
GI 52
Serving size 50 g
Available carbohydrate 20 g
GL 11

Mexican wheat tortilla
GI 30
Serving size 50 g
Available carbohydrate 20 g
GL 6

What’s ‘nixtamalization’?
Thanks to wonderful Wikipedia, here’s a definition. ‘It is the process whereby dry maize grain is soaked and cooked in an alkaline solution, usually limewater, to cause the transparent outer hull, the pericarp, to separate and be removed from the grain. This process has several benefits including enabling the grain to be more effectively ground; increasing protein and vitamin content availability; improving flavor and aroma and reduction of mycotoxins. In the Aztec language Nahuatl, the word for the product of this procedure is nixtamalli or nextamalli. The term nixtamalization can also be used to describe the removal of the pericarp from any grain such as sorghum by an alkali process.’

New GI values from SUGiRS
Continental™ Wholegrain Pasta & Sauce convenience meals
All servings are 200 grams and were prepared following packet instructions with water, reduced fat milk and margarine.
Manufacturer: Unilever Australasia, Epping, NSW, Australia

New GI values from Glycemic Index Laboratories
SoLo Gi Bars
We published the GI values of SoLo Gi bars in December 2005 GI News. The manufacturers have added a new flavour (Lemon Lift GI 28) to their range and all flavours now come in a smaller 100-calorie size that provides 12-13 g carbohydrate and has a GI of around 23.
Check out their website for nutritional information:

Where can I get more information on GI testing?

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

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

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