Prof Jennie Brand-Miller answers your questions. 
Why are there different GI values for the same thing? It’s very confusing.
If you are a fan of Google (and who isn’t) you’ll find various GI values for the same foods and beverages. I have to say that I have no idea where some values come from. Certainly not any scientific research we have seen in peer-reviewed journals or from the GI test facilities we collaborate with.
First of all, some foods we think of as being the same are actually different. The popular potato: same? No. Different. There are many varieties. Ditto for rice. Back in 2007, when we saw the evidence mounting that it is the potato variety that affects its glycemic impact not the cooking method, we sat down with potato expert Graham Liney, grower Frank Mitolo and Dutch potato breeding company Agrico to put a low GI potato on the table. Three years after the first crop was pulled from the soil, Carisma was internationally certified as the first low GI potato (GI 55). Dr Kai-Lin Ek reports on it here and on what we are doing to identify other low GI potatoes.
Secondly, the testing method matters. A food’s GI value must be measured in people (we call this ‘in vivo testing’) and these days, according to ISO 26642:2010 (the international standard). There is (as yet) no easy, inexpensive substitute test. There are also old GI values from the early days of testing, which brings us to carrots.
Photo courtesy Hachette Australia: The Low GI Family Cookbook
Raw or cooked, carrots are good for you and they won’t send your blood glucose on a roller coaster ride. End of story. Why? Well, not only are they a low GI food (41), they have very few carbs. In fact, to get a hefty portion of carbs from carrots you’d have to crunch through at least 5 cups or 750g (about 1½ lb) at a sitting – a pretty awesome achievement even for carrot lovers. How did the high GI carrot myth happen? Well, they were first tested way back in the early days (1981) – only five people were included in the study, the variation among them was huge, the reference food was tested only once and the result was a very high GI. And it was that early high GI result for healthy foods like carrots (along with watermelon) that became the stick to beat the whole GI concept with for years – and still to this day for the anti-GI stalwarts.
- Lesson One: you can’t win ’em all.
- Lesson Two: A food’s GI value was never meant to offer the only criterion by which it is judged as fit to eat. It’s a useful tool from the nutrition tool box to help you choose more of those smart carbs when creating a healthy eating plan.
Professor Jennie Brand-Miller (AM, PhD, FAIFST, FNSA, MAICD) is an internationally recognised authority on carbohydrates and the glycemic index with over 250 scientific publications. She holds a Personal Chair in Human Nutrition in the Boden Institute of Obesity, Nutrition, Exercise and Eating Disorders and Charles Perkins Centre at the University of Sydney. She is the coauthor of many books for the consumer on the glycemic index and health.
It’s Time to Get Mobile Friendly.
From January 2015, GI News is getting a new look so it will be as easy to read on your phone or tablet as it is on your laptop and desktop. It will also be easier for you to share the stories and recipes you like, print them and Tweet them.
At the same time, we will be moving from Blogger and our base at the University of Sydney to WordPress and the Glycemic Index Foundation. The Foundation, a not-for-profit health promotion charity supported by the University of Sydney and JDRF, can provide us with the ongoing technical support we need.
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– Jennie Brand-Miller, Philippa Sandall, Alan Barclay
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