To Your Health

I am trying to avoid diabetes, which runs in my family, by choosing foods for their low glycemic index. Some of the foods I want to eat because they ought to have a low glycemic index are not on anyone's list. Is there some way to calculate the glycemic index myself?

Q. I am trying to avoid diabetes, which runs in my family, by choosing foods for their low glycemic index. Some of the foods I want to eat because they ought to have a low glycemic index are not on anyone's list. Is there some way to calculate the glycemic index myself?

A. The glycemic index (GI) was developed as a guide to help diabetics choose foods according to the extent to which the food raises the blood sugar level. It is calculated by comparing the rise in blood sugar after a fixed amount of the test food (usually the amount supplying 50 grams of carbohydrate, or 200 calories) compared to a standard food (usually white bread). Several factors go into calculating the GI, and the measured responses of many volunteers are averaged in order arrive at the GI, so it is not a "do it yourself" project. There is a move afoot to include the GI on food labels along with other nutritional information, but there is not yet data on enough foods to make this feasible.

There are some serious drawbacks to choosing foods solely on the basis of the GI. The diets of real people do not consist of meals where single food items are eaten to 50-gram carbohydrate portions, and when different kinds of foods are mixed, the glycemic response is unpredictable. Another big problem is that some foods with the lowest GI cannot be tested because the amount supplying 50 grams of carbohydrate is enormous, simply too much for the test volunteers to consume, which is why you can't find a GI for them. For instance, it would take 5 pounds of broccoli or 20 pounds of endive to provide the 50 grams of carbohydrate needed for a standard test meal.

At the moment the GI is a rather crude yardstick for evaluating food and it may soon be replaced by the Insulin Index, a relatively new concept related to the amount of insulin produced when about 240 calories of a test food is consumed. The Insulin Index is not entirely comparable to the GI, because the protein and fat in food are counted in the calories and these can also stimulate insulin release. This approach is more realistic since, although protein-rich foods tend to produce a low blood glucose response there is not always a correspondingly low insulin response. An exaggerated insulin response to food intake has recently been found to be an independent risk factor for coronary heart disease and is at the root of Type II or "Adult Onset" diabetes.

The GI mostly reflects the carbohydrate and fiber content of a food item, although several other factors have an influence. Among these factors are the cooking method, degree of ripeness of vegetables and fruits, salt content, fat content, protein content, and acidity of the food. These and other factors affect the way you digest your food, which then influences the GI.

The GI of a food is most useful when comparing the various carbohydrates (grains, breads, pasta, sweets), which are broken down directly into glucose and enter the bloodstream rapidly. There are still plenty of exceptions to watch out for and some breads and pastas have a low GI but have a dreadfully high Insulin Index. If you want to compare the GI and the Insulin Index of some foods, go to www.zonehome.com/zlib0025.htm for a chart of 38 foods. Meanwhile, choose a diet that emphasizes fresh vegetables and fruits from the enormous variety of foods available, and don't exclude any wholesome food.

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