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The glycemic index
ranks foods on how they affect our blood glucose levels. This index
measures how much your blood glucose increases in the two or three
hours after you eat.
It compares blood glucose levels
after eating equal carbohydrate portions of foods and ranks them
against a standard, set to equal 100. The standard can be either
glucose or white bread, depending on the researcher.
All the foods in the glycemic index
are high in carbohydrates. That's because foods high in fat or
protein don't cause a significant rise in your blood glucose level.
But some of the foods tested for
their glycemic index—like candy bars—have quite a bit of fat. These
foods appear in a falsely favorable light and are not necessarily
good food choices.
Keeping your blood glucose from
going too high is important to people with diabetes. In 1993 the
Diabetes Control and Complications Trial showed that keeping blood
glucose levels as normal as possible is the best strategy for people
with type 1 diabetes to reduce the risks of complications. More
recently the United Kingdom Prospective Diabetes Study showed that
tight control is equally important to people with type 2 diabetes.
The concept of the glycemic index is
widely used in Australia, Canada, France, New Zealand, and the
United Kingdom. Last year the United Nations FAO/WHO Consultation on
Carbohydrates recommended that "the glycemic index of foods be used
in conjunction with information about food composition to guide food
choices."
While dietitians in the United
States have been generally slower to recommend the glycemic index,
three large-scale and long-term studies have recently given it
considerable support. The prestigious Journal of the American
Medical Association recognized the importance of the glycemic index
two years ago in an article reporting the findings of the Nurses'
Health Study of 121,700 U.S. female registered nurses. The study
concluding that eating foods with a high glycemic index appeared to
be a risk factor for type 2 diabetes.
A similar study of 42,759 male
health professionals reported in Diabetes Care also showed that a
high glycemic load increased the risk for men to get type 2
diabetes. And the journal Pediatrics reported that teenage boys ate
nearly twice as much after a high G.I. meal than after a low one.
Assigning Foods a Number
The really shocking results of G.I. studies are in which foods
produce the highest glycemic response. They include many of the
starchy foods we eat a lot of, including most bread, most breakfast
cereals, and baked potatoes. But table sugar—long believed to be the
worst thing for people with diabetes—isn't as high on the index.
Low glycemic foods include pasta,
oats, barley, beans, and some varieties of rice. Acidic fruits have
low glycemic indexes. Likewise, vinegar and lemon juice—as in salad
dressing—helps reduce the glycemic load.
How do they know all this? Not by
food analysis.
One of the problems with the
glycemic index is that it's so difficult to figure out the glycemic
index of a food. Several factors affect it: the variety of the food,
the processing, the preparation, the type of starch, and, for fruit,
whether it's ripe, juiced, or whole.
Consequently, the food scientists
simply have to test the responses of real people to real food. In
tests that take place before breakfast each subject is tested at
least three times. Each test, including fingerstick blood samples,
is usually taken eight times over a three-hour period.
Each of the test subjects gets the
same amount of white bread, which is the benchmark, and of the test
food. Each portion contains 50 grams of available carbohydrate
(excluding fiber).
Renewed Interest in the United States
Researchers around the world have completed hundreds of G.I.
studies. In 1995 they were summarized as the "International Tables
of Glycemic Index" in the
American Journal of Clinical Nutrition.
Those "International Tables" and the
book Glucose Revolution (the U.S. edition of The G.I.
Factor published in Australia and the U.K.) sparked renewed
interest in the glycemic index in the United States among many
people with diabetes. And now, two popular diet books have
incorporated glycemic index findings into their eating plans.
The first to make use of the
glycemic index in a weight loss program was Michel Montignac in
France. This year Erica House in Baltimore published his Eat
Yourself Slim in the United States.
H. Leighton Steward, the lead author
of Sugar Busters!: Cut Sugar to Trim Fat acknowledges his
debt to Montignac. Published in 1998 by Ballantine Books, Sugar
Busters! has been near the top of the best seller lists for a year.
There are, of course, other
considerations in choosing foods besides its glycemic index,
including the amount of fat, fiber, and sodium. While keeping those
considerations in mind, the glycemic index can, however, help you to
eat a more healthy diet by making substitutions so that you eat
foods that are lower on the glycemic index, and therefore have a
lower impact on your blood sugar levels.
For Further Information: See two web
pages written by Rick Mendosa, the author of this article. They are
http://www.mendosa.com/gi.htm and
http://members.lycos.co.uk/ramendosa//gilists.htm.
This article appeared originally on the DiabetesWebSite.com, which
is no longer on-line.
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