What exactly is the Glycemic Index? DR RAJEN M. gives a definition that is easy to follow as he talks about its effectiveness in helping identify food with the effect on blood sugar.

ALL carbohydrates become sugar. It is just a matter of how fast the change takes place. Some become sugar very quickly. Others are slow to digest. They push up blood sugar slowly.

Sugar is a good source of energy. However, it has a huge drawback. In high doses, it is toxic. That is why your body will never store excess sugar.



Your body performs best when your blood sugar is kept relatively constant. If your blood sugar drops too low, you become lethargic and hungry. This condition is called hypoglycemia.

If your blood sugar goes too high, there is tissue damage. This is a crisis situation as prolonged tissue damage causes death. You secrete more insulin. Insulin lowers blood sugar. It converts excess sugar to stored fat.


• Roller Coaster Effect

A fast rise in blood sugar forces your body to produce a large amount of insulin. Thus, when you eat foods that cause a large and rapid rise in sugar, you may feel an initial elevation in energy and mood as your blood sugar rises.

However, this is followed by a cycle of increased fat storage, lethargy, and more hunger. Remember, how you last felt after a heavy banana leaf lunch?

Although increased fat storage may sound bad enough, individuals with diabetes (diabetes mellitus, types 1 and 2) have an even worse problem. They are unable to secrete or process insulin causes their blood sugar to rise too high, leading to a host of additional medical problems.


• Atkins Diet

This is why diets propounded by Dr Robert Atkins, which were very low carbohydrates, were so popular.

By cutting out all carbohydrates which eventually become sugar, you dramatically drop the levels of your circulating blood sugar. Hence, blood sugar comes down as does stored body fat.

However, many find a low or, worse still, no carbohydrate diet difficult to stomach. They may be delighted to know that there is a way to rank carbohydrates by way of an increasingly internationally accepted Gylcemic Index.

The theory behind the Glycemic Index is simply to minimise insulin-related problems by identifying and avoiding foods that have the greatest effect on your blood sugar.

The Glycemic Index is a numerical index that ranks carbohydrates based on their rate of glycemic response (i.e. their conversion to glucose within the human body).

Glycemic Index uses a scale of 0 to 100, with higher values given to foods that cause the most rapid rise in blood sugar. Pure glucose serves as a reference point, and is given a Glycemic Index (GI) of 100.

Glycemic Index values are determined experimentally by feeding human test subjects a fixed portion of the food (after an overnight fast), and subsequently extracting and measuring samples of their blood at specific intervals of time.

The earliest known work on the Glycemic Index was done by Dr David Jenkins and associates at St Michael’s Hospital in Toronto.

More recently, an effort to expand the Glycemic Index has been made by Jennie Brand-Miller and her associates at the Human Nutrition Unit of the University of Sydney in Sydney.


• Glycemic Load

The Glycemic Index compares the potential of foods containing the same amount of carbohydrate to raise blood glucose. However, the amount of carbohydrate consumed also affects blood glucose levels and insulin responses.

The glycemic load of a food is calculated by multiplying the Glycemic Index by the amount of carbohydrate in grams provided by a food and dividing the total by 100.

In essence, each unit of the glycemic load represents the equivalent blood glucose-raising effect of 1 gram of pure glucose or white bread.

In other words, the Glycemic Index talks about the quality and type of the carbohydrate.

The glycemic load, on the other hand, talks about the quantity of the carbohydrate available in a food.

Water melon, for example, is a food rated high in the Glycemic Index as it is high in fibre content and digests fast.

However, the amount of sugar available is low. In other words, it has a low glycemic load. That makes it a relatively good carbohydrate, even on a low carbohydrate programme.


• Lowering Dietary Glycemic Load

Some strategies for lowering dietary glycemic load include:


• Increasing the consumption of fruits, vegetables, legumes (peas and beans), nuts, and whole grains


• Decreasing the consumption of starchy high-glycemic index foods like potatoes, white rice, and white bread


•Decreasing the consumption of sugary foods like cookies, cakes, candy, and soft-drinks.

NEW YORK (Reuters Health) - Assessing a meal using the glycemic index, which lists the quality of carbohydrates contained in many common foods, appears to be a good way to predict the effect a meal will have on blood sugar levels, important information for diabetes, according to the results of a study published in the American Journal of Clinical Nutrition.

Dr. Thomas M. S. Wolever, of the University of Toronto and colleagues examined whether overall carbohydrate content and glycemic index of individual foods, as given in published tables, determined the effects of a realistic mixed meal on the blood sugar in normal subjects.

The team measured the responses to six test meals in 16 subjects in Sydney and eight meals in 10 subjects in Toronto, and then pooled the results. The meals varied in amount of calories, protein, fat, available carbohydrates and glycemic index score.

The blood sugar and insulin responses to the Sydney test meals varied over a 3-fold range. For the Toronto test meals, the blood sugar responses varied over a 2.4-fold range.

The team found no correlation between the blood sugar levels and fat or protein content of the test meal, but there was a significant correlation with carbohydrate content and glycemic index alone, which accounted for 88 percent of the variation in the blood sugar response.

"The good news is that the glycemic index works," Wolever said in a press release. "For sensible people it makes a lot of sense" It uses a "simple proportional measure -- like mixing paint."

SOURCE: American Journal of Clinical Nutrition, June 2006.

Low GI diet may save sight

Age-related macular degeneration (AMD) is one of the leading causes of vision loss in older adults and a person's risk may partly depend upon diet.

When it comes to carbohydrates, quality rather than quantity may be more important, according to new research by Allen Taylor, PhD, director of the Laboratory for Nutrition and Vision Research at the Jean Mayer USDA Human Nutrition Research Centre on Ageing (HNRCA) at Tufts University.

Their findings were reported in the April 2006 issue of the American Journal of Clinical Nutrition.

Taylor and colleagues analysed data from a sub-group of participants in the Nurses' Health Study (NHS) who were enrolled in the Nutrition and Vision Program. The researchers looked at the total amount of carbohydrates consumed over 10 years and the dietary glycaemic index, which is a measure of the quality of overall dietary carbohydrate.

GI linked to risk of vision loss "Women who consumed diets with a relatively high dietary glycaemic index had greater risk of developing signs of early age-related macular degeneration when compared with women who consumed diets with a lower dietary glycaemic index," says lead author Chung-Jung Chiu, DDS, PhD, scientist in the Laboratory for Nutrition and Vision Research at the HNRCA and an assistant professor at Tufts University School of Medicine.

High total carbohydrate intake, however, did not significantly increase the risk factor for AMD.

"In other words, the types of carbohydrates being consumed were more important than the absolute amount," explains Taylor, senior author. A high-glycemic-index diet is one that is rich in high-glycemic-index foods, which are converted more rapidly to blood sugar in the body than are low-glycemic-index foods.

Chiu, Taylor, and colleagues examined the eyes of more than 500 women between 53 and 73 years of age, looking for changes indicative of early AMD. The researchers also analysed the participants' diets, as reported in questionnaires that had been administered periodically over the course of 10 years preceding their eye exams.

Up to double the risk "Dietary glycemic index may be an independent and modifiable risk factor for early AMD," concludes Taylor, who is also a nutrition, ophthalmology and biochemistry professor on the Tufts health sciences campus in Boston. "The likelihood of having abnormalities characteristic of AMD on eye exam more than doubled for women who consumed diets with the highest glycemic index, regardless of other factors already known or suspected to increase the risk of AMD, such as age, high blood pressure, cigarette smoking, and obesity."

AMD primarily and irreversibly affects central vision, which is critical for many activities, such as reading and driving. The disease is caused by the gradual breakdown of light-sensitive cells in the region of the eye's retina called the macula.

Prior to the current study, the association between AMD and dietary carbohydrate had not been evaluated. "We are interested in studying the role of glucose in age-related diseases like AMD," Taylor says, "because evidence suggests that problems with glucose metabolism, as in diabetes, may cause damaging by-products to accumulate in sensitive tissues and contribute to disease."

Other explanations possible "We cannot say, based on these data, whether or not consuming a diet with a high glycemic index causes AMD," says Taylor. He points out that there are other possible explanations for the relationship he and his colleagues observed. "Perhaps a high-glycemic-index diet is a marker for an overall dietary or lifestyle pattern that increases the risk of developing AMD." A diet high in high-glycemic-index foods like white bread and french fries has a higher overall glycemic index than a diet based more heavily on low-glycemic-index foods, such as lentils and yams.

Taylor is cautious in his interpretation of this data, but he believes that further research is critical, as it may ultimately prove helpful in preventing or delaying the onset of such potentially debilitating and costly diseases. – (EurekAlert)

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