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The glycaemic index: a route to better health?

Jane Staniforth examines the preventative role low-glycaemic foods can have in obesity and diabetes, and examines how manufacturers around the world are labelling and marketing these cutting-edge products

Various Western governments have cited obesity and its related diseases as being the major health challenge for the wealthier nations. Indeed, in their joint report ?Carbohydrates in Human Nutrition? published in 1997, the World Health Organization and Food and Agriculture Office of the United Nations (WHO/FAO) stated that, globally, overweight is a bigger problem than undernourishment.

At the same time they also recommended that people in industrialised countries should base their diets on low glycaemic index (GI) foods to prevent the most common diseases of affluence.

What is the GI?
GI is a measurement that expresses a food?s ability to give rise to an increase in blood glucose levels following consumption. The GI figure is measured by testing the blood sugar levels of volunteers after eating a food product that contains 50g of available carbohydrate.

At Reading Scientific Services Ltd (RSSL), measured portions of the food under test are fed to a panel of healthy volunteers after an overnight fast. Finger-prick blood samples are taken at 15-minute intervals over the next two to three hours, and their blood glucose levels are measured. These results give a blood sugar response curve for the two-to-three hour period. This can be compared with the curve derived from consumption of the glucose standard by the same group of volunteers. The average of the GI ratings from all volunteers is considered to be the GI of that food.

Hence the GI is a numerical value given to foods based on their measured potential to raise blood glucose levels relative to the standard. GL (glycaemic load) is a similar dimensionless number that relates the GI of a food item to the amount of carbohydrate it actually contains in a serving.

The difference between GI and GL places the food industry in something of a dilemma, since they are not directly comparable with each other, but both have their merits. Either might be used on product labels, but a combination of both might leave consumers confused, and potentially, misinformed.

It can?t be assumed that the GI value of one brand of cornflakes, for example, will match that of a different brand. Nor is it legitimate to conclude that the GI of a mixed meal will represent an average of its constituent ingredients.

Many dietary factors affect the body?s ability to metabolise glucose and insulin. They include major constituents such as fat and fibre, as well as various mineral, vitamins, fatty acids, hormonal interactions, and an individual?s weight and physical activity.

What is the significance of GI?
While there is no overwhelming weight of evidence, all the evidence so far points to a positive correlation between high-GI diets and the onset of diseases such as type 2 diabetes and cardiovascular disease. Ongoing studies are attempting to clarify the position. These include the Medical Research Council?s ?RISCK study into the impact and amount of dietary fat and carbohydrate on the metabolic syndrome and CVD risk,? which is not due to be completed until November 2005.

In the meantime, the momentum is gathering within the food industry to develop products with a low-GI value. According to where they are produced or sold, they are being variously described as low GI, low-carb, low GL, low glycaemic impact or even ?diabetic friendly,? ?sports friendly? and ?diet friendly,? but these labelling options expose differences in labelling regulations rather than formulation approaches.

GI around the world
The most highly developed market for low GI products is Australia where the GI Symbol Programme (GISP) was launched in 2002. Here, foods can carry the GI symbol, and their GI value, provided they have been tested in an appropriate manner. Interestingly, it is not the GI value alone that permits the GISP symbol to be used. Products must also satisfy nutritional composition criteria in respect of total fat, dietary fibre, sodium, calcium and energy.

In consumer research conducted by GISP in Australia in February 2004, 63 per cent of respondents claimed to be aware of the GI system, 22 per cent had seen the label on foods, and 67 per cent believed they would use the GI to help choose their products.

South Africa also has a GI labelling system, with four very similar logos identifying foods as ?low fat, low GI,? ?lower fat, low GI,? ?lower fat, high GI? and ?lower fat, intermediate GI?. Appropriate occasions for consumption are suggested alongside these logos. Products covered by the scheme include Nestl??s Dialite ice cream, Nature?s Source breakfast cereal, and several products produced by Fine form such as muesli, pasta and bread.

In the USA, the Glycaemic Research Institute has authority to label products according to their GI value, but for a multitude of reasons, the GI concept remains controversial in the US.

The opposite is true in Norway where Dr Fedon Lindberg has championed low GI diets with great success. Market research suggests that 27 per cent of adults in Norway are familiar with the GI concept, and one in four has changed their diet as a consequence. Similarly, the National Food Administration of Sweden has formally endorsed labelling of foods based on their GI and their potential to slow glucose uptake. The first commercial products making this claim are now on the market in Sweden. Elsewhere in Europe glycaemic labelling is becoming popular despite the lack of a clear legal framework.

Adjusting GI
The most obvious and logical approach to lowering the GI of processed foods is to reduce their sugar content, replacing some sugars with low-GI ingredients. However, as with any formulation change, the process is seldom straightforward. Sugars contribute structural, textural and stability attributes to food products, as well as sweetness. The sugar?s role in structure and stability is also relevant during processing as well as in the finished product. There are also legal and labelling issues to consider, and perhaps a re-evaluation of HACCP systems that accompanies any change in formulation or supplier.

Hence any producer looking to reduce the GI of its products is likely to need product development specialists, pilot plant facilities and sensory evaluation/consumer research studies to be sure of producing an acceptable product. They may also need labelling advice and HACCP consultancy.

There is clearly a momentum building in favour of lowering our consumption of foods with a high GI or GL value. That said, it would be wrong to argue that low GI foods are a panacea to all of the industrialised world?s health problems. It would certainly be wrong to select our diet on the basis of GI values alone.

Nonetheless there is every possibility that GI values may soon become a common feature of food labels, and consumers will come to accept a low-GI value as a healthier option. ?Low GI? may soon be as prevalent on food labels as the now commonplace ?low fat? and ?low salt?.

Jane Staniforth is head of food business development at Reading Scientific Services Ltd (RSSL).
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All correspondence will be forwarded to the author.

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