Professor Jennie Brand-Miller answers your questions
Isn’t the insulin response more important than the GI value? Wouldn’t it be better to have an insulin index of foods?
The insulin demand exerted by foods is indeed important for long-term health, but it doesn’t necessarily follow that we need an insulin index of foods instead of a glycemic index. When they have been tested together, the glycemic index is extremely good at predicting a food’s insulin index. (In other words, a low GI food usually has a low insulin index value and a high GI food usually has a high insulin index value.) There are some instances, however, in which a food has a low GI but a high insulin index value. This applies to dairy foods and to some highly palatable, energy-dense ‘indulgence foods.’ Some foods (such as meat, fish, and eggs) that contain no carbohydrate, just protein and fat (and have a GI of essentially zero), still stimulate significant increases in blood insulin.
We don’t currently know how to interpret this type of response for long-term health. It may be a good outcome, because the increase in insulin has contributed to the low level of glycemia. On the other hand, it may be less than ideal, because the increased demand for insulin contributes to beta-cell ‘exhaustion’ and the development of type 2 diabetes. Until studies are carried out to answer these types of questions, the glycemic index remains a proven dietary tool for predicting the effects of food on health.
A recent study in the European Journal of Clinical Nutrition comparing GI and insulinemic index (II) values of carbohydrate-rich foods in healthy people, hyperinsulinemic people and people with type 2 diabetes reports that the GI values are similar regardless of the severity of glycemia or degree of insulin sensitivity, showing that GI is a property of foods and affirming its clinical usefulness in a broad population. Prof Tom Wolever concludes: ‘However, the II values of carbohydrate foods were inversely associated with insulin sensitivity and positively related to the severity of glycemia and hepatic insulin extraction, suggesting that II is not solely a property of foods but also depends on the metabolic status of the subjects.’
GI testing by an accredited laboratory North America
Dr Alexandra Jenkins
Glycemic Index Laboratories
20 Victoria Street, Suite 300
Toronto, Ontario M5C 298 Canada
Phone +1 416 861 0506
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
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