Q. How to calculate glycemic index?
If you take a certain rood and measure the rise in blood sugar in response to the food consumed in comparison with the response to an equal amount of glucose and know the glycemic index in percentage, then it would be a better method of planning diabetic diets. We do have glycemic index of individual food items such as wheat, rice, pulses and vegetables. For example, cereals like wheat, rice, vegetables (potato and carrots) have a high glycemic index (65-75%), fruits have 45-55%, lentils (peas, beans, green gram, Benganl gram) have a low glycemic index (30-40%). Glucose has in glycernic index 100%. So diets with lower glycemiic index are more beneficial for diabetics. These foods generally have a more fibre content. Since we do not take individual foods but two or more foods cooked and prepared, we would be interested in glycemic index of common mixed foods consumed by us in our main meals and also some common snacks. Work is being conducted in various institutions on this area. Some day we will have this data and would be able to switch from food exchange system to glycemic index of cooked food for planning diabetic diets. We call calculate the glycemic index of food by using this formula:
GI = Area under 2 hours blood response curve to test food /Area under 2 hours response for equivalent glucose X 100
You can get some idea of individual raw foods and cooked foods for their glycemic index values from the Table 12.10.
A GI of 70 or more is high, a GI of 56 to 69 is medium and a GI of 55 or less is low.
Thus From our discussion above it is clear that the glycemic index tells us how rapidly a particular carbohydrate turns into sugar. It certainly does not tell us how much of carbohydrate is actually present in a serving of a particular food. This information too is important if we want to assess the true impact of carbohydrate consumption. To know this we need to understand another concept called the glyceinic load The glycemic load of a food is the glycemic index divided by hundred and multiplied by its available carbohydrate content (i.e. carbohydrate minus fibre) in grams. The glycemic toad is a relatively new way to assess the impact of carbohydrate consumption that takes the glycemic index into account, but gives a full picture than doe's glycemic index alone. For example, if we consider watermelon. Watermelon has a high glycemic index (about 72). However, a serving of 120 g of watermelon has only about 6 grams of available carbohydrate per serving. So its glycemic load is pretty low i.e. 72/100 x G = 4.32.
Perhaps suitable for diabetics.
We all know that sugar, honey, jaggery i.e. all sweeteners, which are rich in mono and disaccharides, are completely omitted from the diet of diabetics. However, craving to eat sweet meats is always high among several patients. It is for this reason that diabetics are suggested to use artificial (nutritive/non-nutritive) sweeteners, which usually do not provide any significant amount of calories or other nutrients. Let us now brief ourselves on the commonly used sweeteners.