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The Glycaemic Index: A Physiological Classification of Dietary Carbohydrates.

The Glycaemic Index: A Physiological Classification of Dietary Carbohydrates.

Wolever TMS. Cabi Publishing, Oxfordshire, UK, 2006, 272 pages, 60 pounds, ISBN 1-84593-0517

So, you think you know everything you need to know about the glycaemic index (GI), glycaemic load (GL) and glycaemic response? You may be surprised ...

The seminal paper 'Glycemic index of foods: a physiological basis for carbohydrate exchange' was published in the American Journal of Clinical Nutrition in March 1981. Along with Dr David Jenkins, Tom Wolever was one of the co-inventors of the glycaemic index concept. As the title of the paper suggests, the GI was originally invented to 'correct' carbohydrate exchanges so that they more closely reflected the physiological response of people with diabetes to carbohydrates in foods, and was envisaged to be only of use to that particular group of people. Over 25 years later, several thousand studies from around the world have examined the accuracy, reliability, validity, epidemiological associations with chronic disease, and clinical utility of the GI concept. Throughout this time period, Professor Wolever has been one of the main driving forces behind this research.

It was only in 1997 that the glycaemic load (GL), which is the product of the GI multiplied by the amount of available carbohydrate (GL = GI (%) x available carbohydrate), was conceptualised by the nutritional epidemiologists at Harvard University in the USA.

In the past 10 years, both the GI and the GL have captured the imagination of researchers, clinicians and lay people alike, triggering a dramatic upsurge in scientific research into carbohydrate metabolism, and much popular debate.

Perhaps to mark the end of the first 25 years of GI research, Professor Wolever has written this comprehensive review and analysis of most, if not all, the research into the GI and the GL.

The journey starts with a brief history of the scientific investigation of the effect of carbohydrates on health going back 150 years. The author then very carefully defines GI, explaining clearly why it is not the same as glycaemic response. While at first glance this may not sound all that ground breaking, it is this very issue that is one of the major underlying causes of much of the current confusion about the measurement, and clinical utility of both the GI and GL. Following this, we are given an in-depth description of how to determine the GI of a food accurately and reliably, with careful consideration of the factors which do and do not affect the final result.

Many people may also have heard of the insulin index, and thought that, due to the hormone's central role in fuel metabolism, it is probably more important than either the GI and GL? Professor Wolever meticulously analyses the current techniques used to assess insulin metabolism, and compares and contrasts it to glucose metabolism and the GI. The result will surprise many ...

Next, we visit the much vexed issue of the use of the GI in mixed meals. As well as critically reviewing the published data on the topic, Professor Wolever demonstrates his mathematical prowess by re-analysing the published data from around the world, so that we are comparing like with like. These data provide compelling evidence that the GI of mixed meals can be predicted with an acceptable degree of accuracy to enable its clinical use.

From here the book traces the role of the GI in the promotion of good health through improvements in physical and mental performance, as well as the prevention and management of overweight and obesity.

Finally, he explores the complex relationship that is emerging between GI and chronic disease risk. The evidence linking the development of type 2 diabetes, cardiovascular disease and certain cancers is critically examined, and suggestions for further areas of research are put fourth.

Targeted squarely at health professionals, this book is truly the definitive summary of research into the GI, GL and glycaemic carbohydrate. In fact, if anything, some will find it just a little too detailed and may find the complex mathematical proofs a little overwhelming. However, it is an absolute must for anyone conducting serious research in to the area of glycaemic carbohydrate, and a great resource for anyone interested in this much debated and often misunderstood concept.

Alan Barclay, APD

PhD Candidate, University of Sydney

Sydney, New South Wales, Australia
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Author:Barclay, Alan
Publication:Nutrition & Dietetics: The Journal of the Dietitians Association of Australia
Date:Sep 1, 2007
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