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The glycemic index: why everyone's talking about it

By David Mendosa

Last Update: August 7, 2001

To say that everyone is talking about the glycemic index may be an exaggeration, but judging by book sales, millions of people are reading about it.

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Judging by what is being written about the glycemic index, it also is changing the way millions of people feel and leading many experts to rethink some fundamental concepts about food.

Good carbs, bad carbs
The glycemic index is a list of foods. It rates carbohydrate foods by comparing how much they raise blood sugar after eating a measured portion of the food compared to a reference food set to equal 100. The reference can be either glucose or white bread, depending on the researcher. All the foods in the glycemic index are high in carbohydrates. Foods low in carbohydrates and high in fat or protein don't cause a significant rise in blood sugar, so researchers don't bother to measure them.

Studies have shown that low glycemic index diets are associated with a lower risk of developing diabetes and heart disease. This dual effect on two of the leading killers of our day, together with the reported benefits for weight loss, is why interest in the glycemic index has caught fire with a wide cross-section of the public.

Studies have shown that low glycemic index diets are associated with a lower risk of developing diabetes and heart disease. This dual effect on two of the leading killers of our day, together with the reported benefits for weight loss, is why interest in the glycemic index has caught fire with a wide cross-section of the public.

How fast a food raises blood sugar is important, because it determines how much insulin is produced to keep the blood sugar from going too high. For some people, this isn't an issue. However, some people will produce an excess of insulin in response to high glycemic index foods, and that's where the trouble starts.

Insulin reduces blood sugar by sending it out of the blood and into the cells to be stored as fat. If there's too much insulin, then after the blood sugar goes up, the excess insulin causes it to fall too low, which can create the rollercoaster effect of a temporary lift, then fatigue and carbohydrate cravings.

Overconsumption of high glycemic index foods also appears to contribute to insulin resistance and diabetes, as well as an impressive list of common health problems, all of which result from the long-term effects of too much insulin in the body.

A simple tool for making better choices
Using white bread as the standard, sucrose (table sugar) has a glycemic index of 92. So white bread, with a glycemic index of 100, raises blood glucose slightly faster than table sugar. Baked potatoes may be the biggest surprise, with a glycemic index of 121, which is 29 points higher than table sugar!

Proponents claim that using the glycemic index in making food choices can help you lose weight, reduce your risk of heart disease, improve your energy level and athletic performance, stabilize your blood sugar and enjoy greater overall wellness.

For high glycemic baked potatoes (121), you can substitute pasta, prepared slightly al dente (typically 50 to 60), beans and legumes (typically 40 to 60) or sweet potatoes (77), all of which have less of a glycemic effect. Instead of regular rice (126), you can substitute basmati (83) or Uncle Ben's Converted Rice (63), or for part of the rice, substitute the much lower glycemic pearled barley (36). Instead of highly processed breakfast cereals, cookies, crackers, cakes and muffins, look for those made from unrefined cereals or those that add dried fruits, which have a lower glycemic index than refined flour. Instead of tropical fruits such as bananas (77) switch to temperate climate fruits such as apples (54) or peaches (60).

A parade of best selling books

These recommendations are consistent with what Jennie Brand-Miller, Ph.D. and her co-authors teach in The Glucose Revolution: The Authoritative Guide to the Glycemic Index, published for the first time in the United States in 1999. Earlier editions, titled The G.I. Factor, were published in Australia and then in the United Kingdom.

Barry Sears, Ph.D., author of the 1995 bestseller The Zone, agrees. His 40-30-30 approach recommends moderate carbohydrate intake (about 40 percent of total calories) and replacing higher glycemic index foods with ones lower on the scale. His goal is to reduce what he calls the "glycemic load", or the combination of the total intake of carbohydrates and their rate of entry into the bloodstream.

Dr. Andrew Weil makes recommendations based on the glycemic index in Eating Well for Optimum Health. He points out that in cultures in which the traditional diet is still eaten and in which many of civilization's most common diseases are practically nonexistent, most of the staple foods are low glycemic index carbohydrates, in contrast with the high glycemic index carbohydrates that pervade the standard American diet.

The 1998 bestseller Sugar Busters! by three New Orleans doctors and a business executive also uses the glycemic index. Sugar Busters draws from Michel Montignac's 1986 weight loss study based on the glycemic index published in France in 1986. His Eat Yourself Slim was published in the United States in 1999.

The first U.S. popularizations of the glycemic index for weight loss were two slim books that appeared in 1993 and 1994. They were The G-Index Diet by Dr. Richard N. Podell and The Good Calorie Diet by Philip Lipetz, Ph.D.

In fact, most of the diet bestsellers of recent years make recommendations based on the principle behind the glycemic index—variations in the way different foods raise blood sugar and stimulate insulin, even though not all of them specifically use the glycemic index as a tool. These include Dr. Atkins' New Diet Revolution by Dr. Robert C. Atkins, Protein Power by Drs. Michael R. and Mary Dan Eades, The Carbohydrate Addicts' Diet by Drs. Rachael and Richard Heller, The Schwarzbein Principle by Dr. Diana Schwarzbein and Syndrome X by Dr. Gerald Reaven.

Growing body of research
All of these books are based at least in part on scientific studies that showed different foods producing different blood glucose levels. The first professional paper to use the term "glycemic index" was by Dr. David J.A. Jenkins of the department of nutrition and food science of the University of Toronto and nine co-authors. The March 1981 issue of The American Journal of Clinical Nutrition published this paper as "Glycemic Index of Foods: A Physiological Basis for Carbohydrate Exchange."

Jenkins and his associates tested 62 commonly eaten foods for their blood glucose response—that is, how high these foods raised the blood glucose levels of their test subjects. These 62 foods are still the only ones cited in many popular articles, although by now, researchers around the world have completed testing of more than 300 different foods.

Although the American public is making widespread use of the glycemic index, among nutritional authorities, the scientific concept is much more widely used in Australia, Canada, France, New Zealand and the United Kingdom than it has been in the United States.

Although the American public is making widespread use of the glycemic index, among nutritional authorities, the scientific concept is much more widely used in Australia, Canada, France, New Zealand and the United Kingdom than it has been in the United States. In 1997, the United Nations Food and Agriculture Organization/World Health Organization Consultation on Carbohydrates recommended that "the glycemic index of foods be used in conjunction with information about food composition to guide food choices."

Even in the United States, several large-scale and long-term studies in recent years have begun to give support to the glycemic index. The Journal of the American Medical Association recognized the importance of the glycemic index three years ago in an article reporting the findings of the Nurses' Health Study of 65,173 U.S. female registered nurses. The study concluded that eating foods with a high glycemic index appeared to be a risk factor for Type 2 diabetes. The article is Jorge Salmerón et al., "Dietary Fiber, Glycemic Load, and Risk of Non-Insulin-Dependent Diabetes Mellitus in Women," JAMA 1997 Feb 12;227(6):472-7).

A study of 42,759 male health professionals reported in Diabetes Care likewise showed that a high glycemic load increased the risk for men to get Type 2 diabetes. The abstract of the study, by Jorge Salmerón et al., is titled "Dietary Fiber, Glycemic Load, and Risk of NIDDM in Men" Diabetes Care 1997 April; 20(4):545-50.

Differences of opinion
A registered dietitian named Barbara Barry wrote in the July/August 1995 issue of Diabetes Self-Management that "all sugars are created equal in terms of your blood glucose control." Outside the diabetes field, many dietitians respond to the glycemic index by insisting that only total calories matter and that "a calorie is a calorie, whether it comes from carbohydrates, protein or fat."

However, there is growing evidence that a low glycemic diet has benefits. For heart disease and especially to prevent it, a low glycemic diet can reduce the risk by helping to reduce body weight and improve blood glucose. In the Harvard Nurses' Study, those who ate a low glycemic diet had half the risk of heart attacks compared to those on the highest glycemic diet.

For weight loss, low glycemic foods have two advantages, Brand-Miller wrote. "They fill you up and keep you satisfied for longer," and "they help you burn more of your body fat and less of your body muscle." It is these features that are behind the phenomenal success of the Sugar Busters! and similar diets.

Special rules for athletes
The picture is more complicated for athletes, but the glycemic index can still provide a valuable edge—there are times when low glycemic foods provide an advantage and times when high glycemic foods are better.

Just before a race or other athletic event, high glycemic foods, like potatoes, will produce a rapid increase in glucose and insulin levels. That's not desirable, Brand-Miller said. The high glycemic meal will only produce a temporary supply of energy—a surge and then a letdown.

Low glycemic foods like pasta, which are digested and absorbed more slowly, are able to provide glucose to the working muscles by the end of the exercise, when glycogen stores are running low.

"They can be likened to a continuous injection of glucose during the event," she wrote. "This can boost energy when fatigue begins to set in."

After the event, high glycemic foods are better because they stimulate more insulin. The insulin helps put glycogen back into the muscles.

There are, of course, other considerations in choosing foods besides the glycemic index, including the amount and type of fat and the amount of fiber and sodium, and there are differing schools of thought on what proportions of carbohydrates, protein and fat are best. While keeping those considerations in mind, the glycemic index can help many people to eat a more healthy diet by making substitutions that favor foods that are lower on the glycemic index and therefore have less impact on blood glucose and insulin levels. 

This article originally appeared on on November 10, 2000.

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