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The Glycemic Index

By David Mendosa

Last Update: January 12, 2001

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.

Vinegar and lemon juice…reduce the glycemic load.

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—help 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 other web pages written by David Mendosa, the author of this article. They are http://www.mendosa.com/gi.htm and http://www.mendosa.com/gilists.htm. 


This article appeared originally on the DiabetesWebSite.com, which is no longer on-line.


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