Tweaking GI as a food value

25 March 2014

by Dr John Monro

Type 2 diabetes is not a particularly obvious or overt condition, and many with diabetes are unaware that they have it until they are found to have elevated blood glucose concentrations (hyperglycaemia) – a defining diagnostic feature of the disease.

The battle against diabetes needs to be multi-pronged, and this should be reflected in the research we do:

  • Development of simple, but precise and accurate, laboratory tests of how foods affect the body’s blood glucose levels (glucose loading).
  • Use of the tests to select prototypes during the development of new products.
  • Generation of new food values that represent glucose loading that can be used by consumers to make healthy food choices.

Of particular importance, is generating new food values that represent glycaemic impact. The reason for needing new food values may not be immediately obvious. After all, we have the glycaemic index (GI), which is being increasingly used as the parameter with which to compare the glycaemic potencies of foods.

There are, however, a number of problems with such use of GI, especially by shopping consumers. Firstly, the so-called “GI of a food” is not in fact a food GI, but a GI of one component in food, the carbohydrate. So the terminology is incorrect and misleading. GI indicates the relative glycaemic effect of foods only if the food quantities being compared contain equal amounts of available carbohydrate. But across foods in the supermarket, and even within food categories, this is rarely the case. Secondly, GI is an index value, so it does not change as a function of carbohydrate content or food intake. Whether you have two, four or six Weetbix for breakfast, the GI value remains the same. So GI gives no idea of the effect of portion size or of food intake on glycaemic effect. There are additional problems in how GI is measured clinically (low subject numbers) as well as its accuracy and precision.

We have approached these problems in a variety of ways. To address the problem of precision, we have developed laboratory tests that measure the main glycaemic property of foods: how much carbohydrate is actually available for absorption in the gut. We’ve done this in a highly reproducible manner. We have addressed accuracy by building in physiological corrections to account for the change in the blood glucose response depending on intake (dose-dependency). The results we get are also correlated strongly with clinical measurements made on amounts of cereal products that customers generally consume.

The procedure has not been perfected yet, but as we continue our research into the way that various food components and structures influence digestive processes we will be able to further “tweak” what is already proving to be a useful and economical tool in the development of healthier foods of reduced glycaemic impact.

Originally published on the Riddet Foodlink website.

Emma Timewell
Communications Manager, Corporate Communications,
Plant & Food Research Mt Albert,
120 Mt Albert Road, Sandringham
Auckland, 1025, New Zealand
Telephone: +64-9-925 8692
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