The Importance of the Glycaemic Index (GI)

Most Asians eat a healthy diet. However, it may be surprising to learn that there is an increased risk of diabetes, heart disease, and weight gain in Asians largely due to the high carbohydrate diets that we consume and the type of carbohydrates we consume.

This fact may sound confusing but scientific evidence from clinical trials in prestigious laboratories in the US and UK advocate the consumption of what is known as a low-Glycemic Index diet (GI). A low-GI diet has become the new nutritional revolution in Australia, Scandinavia, Canada, and more recently, the UK.

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What is a Low-GI Diet?

Carbohydrates can be divided into 3 main groups – simple sugar molecules, medium length chains of sugar molecules, and very long and complex combinations of sugar molecules. The Glycemic Index concept came about when scientists studied how the body breaks these different types of carbohydrates down when they are included in the diet.

The Glycemic Index (GI), first introduced by Jenkins and colleagues in 1981, is the classification of the blood glucose-raising potential of carbohydrate foods. It is defined as the incremental area under the blood glucose curve of a 50g carbohydrate portion of a test food expressed as a percentage of the response to 50g carbohydrate of a reference food (usually glucose solution) tested on the same subject on a different day.

The principle is that the slower the rate of carbohydrate absorption, the lower the rise in blood glucose level and the lower the GI value.

High, Medium and Low

High-GI foods are characterised by fast-release of carbohydrates and higher blood glucose levels. A GI value of 70 or more is considered high, one of 56-69 is medium and one of 55 or less is low when compared to glucose, which has a GI value of 100.

Surprisingly, glucose solution and baked potato containing 50 g of available carbohydrate give similar glycemic response. This means that although potatoes are rich in very complex carbohydrates, the body reacts to them by producing almost the same levels of glucose as it does when the diet is glucose by itself.

This indicates that the conventional classification based on structure as simple and complex carbohydrates is not necessarily related in the same way to the blood glucose response generated after their consumption.

GI Values

The scientific literature shows that the metabolic effects of low-GI diets induce weight loss, lower fasting glucose and insulin levels, reduce triacylglycerol (TAG) levels and improve blood pressure. The GI values of over 2,500 'Western' foods have been tested and published so far. Currently there are limited published GI values for 'Asian' foods, although this list is expanding. A selection of GI values is listed for some representative foods.

* Boiled potato 100
* Jianxi rice vermicelli, boiled 56
* White bread 70
* Mung beans 31
* Banana 88
* Mung bean noodles 39
* Orange Juice 75
* Rice noodles, fresh 40
* Apple 55
* Rice noodles, dried 61
* Skimmed milk 46
* Basmati rice 55
* Whole meal flour 67
* Broken rice 86
* All bran 38
* Glutinous Rice 94
* Muesli 81
* Jasmine rice 109
* Maize meal porridge 55
* Sushi 67
* Lentils 35
* Rice cracker 111
* Apricots 61
* Udon (Japanese wheat noodles) 58
* Orange 42
* Soba (buckwheat noodles) 56
* Mango 51
* Chinese noodles 47
* Papaya 58
* Pear 37
* Linola seed bread 90
* Butter beans 30
* Croissant 67
* Taiwan vermicelli, boiled 68

Other Factors

The GI of foods depends on many factors, including particle size, cooking, food processing, other food components present (e.g. fat, protein, dietary fibre), the proportion and type of sugars and starch, and the structure of starch.

Consequently, there is considerable variation in GI of the same food manufactured in different countries. Food manufacturers have developed a range of low GI foods by varying the ingredients used or altering the processing conditions. The consumption of diets with low GI may therefore be an important strategy in the prevention and management of diabetes and other chronic diseases.

The use of common Japanese ingredients such as vinegar, dairy products, and bean products were found to significantly reduce the GI of rice when ingested together, before or after a meal. Noodles such as udon, soba, and spaghetti also show low GI values.

The use of novel or natural food ingredients (wheat fibre, wheat germ, mustard seeds, sesame seeds, linseed, beta-glucan) to alter glycemic response has now become a well-established process in food technology. Over a 24-hour period, a reduction in glucose profile can be achieved following a simple change to the diet, namely the substitution of a high GI food to a low GI food.

Managing Diabetes

Replacing high GI forms of carbohydrate with low GI carbohydrates may not only reduce the risk of type 2-diabetes, but also be an additional health benefit to those who are managing diabetes by diet control.

The consumption of diets with low GI may therefore be an important strategy in the prevention and management of diabetes and other chronic diseases. Given the high prevalence of diabetes and cardiovascular disease in Asia, the manufacture and identification of foods with low GI is of major public health imperative.

A study in Thailand has shown that consumption of mung bean noodles with low GI can improve diabetic control in type 2 diabetes. Many traditional starchy foods (rice) may have higher GI values than expected but low GI staples such as rice noodles may be preferable for diabetics as shown from a study on Vietnamese foods in Australia.

Irrespective of the favourable features of Chinese diets such as low fat content, plenty of vegetables and rice-based than potato-based, the prevalence of type 2 diabetes is increasing among the Chinese population. Excessive caloric intake from fast food, insufficient exercise, increased reliance on automobiles and popularisation of television are some of the factors that have contributed to this upward trend in diabetes and obesity.

Knowledge about GI value of Asian foods may assist in the development of better dietary advice for individuals with diabetes and obesity and will aid further research into the application of GI.

More info on GLYCAEMIC INDEX here.

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