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GLYCEMIC INDEX |
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CHENNAI, INDIA, Jun. 21 -/E-Wire/--
"Let food be thy medicine, thy medicine shall be thy food", said Hippocrates, the father of medicine several thousand years ago. Unfortunately these days, man adopts himself to a sedentary lifestyle where his mental activity leaves behind his physical activity. As a result, man has become divorced from nature and its rich beautiful bounty.
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Research and development in Food science and technology has had a fundamental impact on the way people live. Many people have become more health conscious these days. A balanced diet is a wise choice for sound health. It means eating foods and drinks in the right amounts and proportions from all the five basic food groups. The first category under the basic five food group system developed by the Indian Council of Medical Research (ICMR) is Cereal grains and products. Among the cereals, 'rice' is commonly consumed by us, as it stands out as the staple food of South Asia. Being the chief contributor of carbohydrates, rice also provides vital other nutrients such as the 'B' vitamin, that provide additional health benefits to our body.
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Carbohydrates that break down rapidly during digestion, are absorbed and metabolized quickly have the highest 'Glycemic index'. Certain carbohydrates break down slowly. This means that they are absorbed and metabolized slowly and hence the glucose is gradually released into the blood stream. Such foods will have a low Glycemic index. (Glucose is a simple sugar, and comes under the classification of carbohydrates).
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WHAT IS GLYCEMIC INDEX?
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'Glycemia' is the presence of glucose in the blood. Blood glucose rises after a meal. This does not merely depend on the amount of carbohydrate ingested but also the rapidity of absorption which varies with fibre content, type of starch in the food etc. The ability of the food item to raise blood glucose is measured in terms of its Glycemic index. In other words GI is a scale that ranks carbohydrate – rich foods by++ how much they raise blood glucose levels compared to a standard food. The standard food is glucose or white bread. It is more to do with the quality of carbohydrate than its quantity.
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GI is a ranking system for carbohydrates based on their effect on blood glucose levels in the first two hours. It compares gram for gram carbohydrate in individual foods providing a numerical evidence based index of postprandial (post meal) glycemia (Jenkins et al., 1981) The Glycemic index of a food is defined by the area under the 2 hour blood glucose response curve (AUC) following the ingestion of a fixed portion of carbohydrate (usually 50 g). The AUC of the test food is divided by the AUC of the standard (either glucose or white bread) and multiplied by 100.
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A lower Glycemic index suggests slower rates of digestion and absorption of the sugars and starches in the foods and may also indicate greater extraction from the liver and periphery of the products of carbohydrate digestion.
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FACTORS AFFECTING GLYCEMIC INDEX
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Glycemic index depends on a number of factors such as • The type of starch (Amylose vs Amylopectin) • Locking up of starch molecules within the food. • Dietary fibre ( Soluble) and resistant starch. • Fat and protein content of the food. • Acidity of the meal (Adding vinegar for example, will lower the GI).
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HOW IS THE GI MEASURED? The glycemic index (GI) is a measure of the power of foods (or specifically the carbohydrate in a food) to raise blood glucose (sugar) levels after being eaten. The GI values of foods must be measured using valid scientific methods. It cannot be guessed by looking at the composition of the food. Currently, only a few nutrition research groups around the world provide a legitimate testing service. Professor Jennie Brand-Miller at the Human Nutrition Unit, Sydney University has been at the forefront of glycemic index research for around two decades, and her research group has determined the GI values of over a thousand foods. The GI value of a food is determined by feeding 10 or more healthy people a portion of the food containing 50 grams of digestible (available) carbohydrate and then measuring the effect on their blood glucose levels over the next two hours. For each person, the area under their two-hour blood glucose response (glucose AUC) for this food is then measured. On another occasion, the same 10 people consume an equal-carbohydrate portion of glucose sugar (the reference food) and their two-hour blood glucose response is also measured. A GI value for the test food is then calculated for each person by dividing their glucose AUC for the test food by their glucose AUC for the reference food. The final GI value for the test food is the average GI value for the 10 people. Foods with a high GI score contain rapidly digested carbohydrate, which produces a large rapid rise and fall in the level of blood glucose. In contrast, foods with a low GI score contain slowly digested carbohydrate, which produces a gradual, relatively low rise in the level of blood glucose.
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CLASSIFICATION OF FOODS ACCORDING TO THE GLYCEMIC INDEX
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The classification of foods according to low GI is given below.
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Low GI
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55 or less: Most fruit and vegetables (but not potato), Moolgiri rice, oats, all bran
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Medium GI
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56-69 : Sucrose, Whole wheat, potato, sweet corn, pop-corn High GI
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70 or more : Corn flakes, baked potato, Jasmine rice, White bread, White rice, Basmati Rice
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A low GI food will release glucose slowly and steadily. A high GI food will provide a rapid rise in the blood glucose levels and is suitable for energy recovery after endurance exercise or for a diabetic person experiencing hypoglycemia.
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ADVANTAGES OF LOW GLYCEMC INDEX DIET
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• Helps people lose and manage weight. • Increase the body's sensitivity to insulin. • Improve diabetes management. • Reduces the risk of heart disease. • Improves blood cholesterol levels. • Helps you to manage the symptoms of polycystic ovarian disease (PCOD). • Reduce hunger and keep you fuller for longer. • Prolong physical endurance. • Help re-fuel carbohydrate stores after exercise.
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Choose low GI foods to give you sustained energy for a longer period of time!
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This article is contributed by Dr. Trevor, B.Appl.Sc. (Hons) M.A.I.M., M.R.A.C.I., and Miss. S. Sona, M.Phil 'Foods and Nutrition'. Dr. Trevor is the Vice President for Pen Foods Pvt Ltd and Miss S. Sona is the Technical Manager, Pen Foods Pvt Ltd.
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