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The Glucose Puzzle

The Glycemic Index Pro and Con

By David Mendosa

It's controversial, often misunderstood, and even somewhat mysterious in the way it works. Some people swear by it; others swear at it.

Table sugar…isn't as high on the index.

It's called the glycemic index. It simply ranks foods on how they affect our blood sugar levels. This index measures how much your blood sugar increases in the two or three hours after you eat.

It compares blood sugar 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 your blood sugar level to rise much.

Keeping your blood sugar 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. Last year the United Kingdom Prospective Diabetes Study showed that tight control is equally important to people with type 2 diabetes.

So if following the glycemic index helps keep blood sugar from going too high why don't diabetes educators and dietitians teach this concept to all of us?

In fact, the concept 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."

Even in the United States three large-scale and long-term studies have given considerable support to the glycemic index in the past couple of years. 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 likewise showed that a high glycemic load increased the risk for men to get type 2 diabetes. And just a few months ago the journal Pediatrics reported that teenage boys ate nearly twice as much after a high G.I. meal than after a low one.

The really shocking results of glycemic index studies are what 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. 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. It's not something that anyone could predict. That's because too many factors affect it: the variety of the food, the processing, the preparation, the type of starch, and for fruit whether it's ripe or not, juiced or whole.

Consequently, the food scientists simply have to test the responses of real people to real food. 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). The tests take place before breakfast, and each subject is tested at least three times. Each test including fingerstick blood samples usually taken eight times over a three-hour period.

Even the individual test subjects will have somewhat different responses from day to day, admits Dr. Thomas Wolever of the University of Toronto, one of the pioneers and among the most outspoken advocates of glycemic index testing. Along with Dr. David Jenkins, he was a co-author of the first published glycemic index study in 1981.

Subsequently, researchers around the world 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.

Professor Jennie Brand-Miller of Australia's University of Sydney, who authored the "International Tables," chose Dr. Wolever to be the North American co-author of her forthcoming book Glucose Revolution. To be published this summer by Marlowe & Company in New York, it will finally make available here an American version of The G.I. Factor, which has gone through three editions in Australia and the U.K. since 1996.

It was those "International Tables" and this book that sparked renewed interest in the glycemic index in the United States among many people with diabetes. And that's the other problem.

Few American diabetes educators and dietitians are persuaded to use the glycemic index in clinical practice. They have several reservations.

A registered dietitian named Barbara Barry writing in the July/August, 1995, issue of Diabetes Self-Management even goes so far as to claim that "all sugars are created equal in terms of your blood glucose control." Other advocates of carbohydrate counting have echoed that statement.

But even some of the sharpest critics of the clinical use of the glycemic index dissent from that view. "That's not true," says Marion Franz, a registered dietitian and Certified Diabetes Educator and Director of Nutrition and Professional Education at the International Diabetes Center, Minneapolis. "They are not all equal; different carbohydrates will give different responses."

Ms. Franz was the lead author of the 1994 Technical Review that concluded that "recommending only foods with a low glycemic response severely limits food choices." It also said, "First priority should be given to the total amount of carbohydrate consumed rather than the source of the carbohydrate."

That Technical Review helped set the basis of the American Diabetes Association's Position Statement on nutrition. While recognizing that "various starches do have different glycemic responses," the Position Statement echoed the Technical Review's emphasis on amount of carbohydrates eaten.

While the ADA has been no supporter of using the glycemic index in clinical practice, "I don't think we have a specific negative position on the glycemic index," says ADA President Gerald Bernstein, M.D. " And there is no question that there is difference among different carbohydrates."

If different carbohydrates are generally recognized as affecting us differently, then why not follow the glycemic index in practice? The objection stated most frequently has to do with mixed meals. Here are two separate but related objections—predictability and ease of use.

"The G.I. of a carbohydrate may be different when it is eaten alone or as part of a mixed meal," writes Dr. Alan Rubin, a San Francisco endocrinologist, in his forthcoming book Diabetes for Dummies. Dr. Rubin is nevertheless a proponent of switching to low G.I. carbohydrates.

A registered dietitian and Certified Diabetes Educator, who says up front that she is not a proponent of using the glycemic index for managing blood glucose, has the same objection. "Once you begin combining foods, the G.I. of individual foods really no longer is valid," says Mary Austin, a member of the American Association of Diabetes Educators board of directors. "Most people do eat mixed meals, and we are not convinced that in a mixed meal it tells you a whole lot of anything."

Not true, writes Dr. Brand-Miller in the forthcoming edition of her book. "We can still apply the glycemic index to these real meals even though the G.I. values are originally derived from testing single foods in isolation. We found two-fold differences in glycemia among six different mixed meals containing the same amount of carbohydrate, fat, and protein."

Diabetes educators have also been reluctant to teach it because they believe it is hard to understand and will create confusion, Dr. Rubin says. Indeed, "For the average person trying to teach themselves it would be very difficult," says Lois Maurer, a registered dietitian, Certified Diabetes Educator, and AADE board member. "We don't want to overwhelm them."

It's tedious to calculate the glycemic index of a mixed meal, says Gail Frank, a registered dietitian, media spokesperson for the American Dietetic Association, and a professor of Nutrition at California State University Long Beach. When you go to make a sandwich, for example, "There aren't copious tables that list all these foods."

The problem for most registered dietitians, says Ms. Austin, is that they have so little time to spend with each person. "Quantity, quality of foods, their whole diet," she says, "there are so many things that come before worrying about the glycemic index of individual foods that with a lot of patients I don't get to that point."

On the other hand, the argument that the glycemic index is hard to understand and might create confusion is "about as lousy an argument as you can come up with," exclaims Dr. Tom Dorsch, an endocrinologist in Peoria, Illinois. "It seems to me that teaching people how to count carbohydrates and add all this up in your head is a whole lot more confusing than when you say that when you eat a piece of watermelon your sugar is going to go up higher than when you eat an apple. I understand all the scientific problems with it, but then to toss it out and then to say it's no good is beyond me," Dr. Dorsch concludes.

Ms. Maurer wouldn't throw out the glycemic index. But she believes it makes sense only for the most highly motivated particularly women with gestational diabetes. Ms. Franz concurs that the glycemic index has a role in gestational diabetes, but is otherwise "reluctant to add one more variable. We have simplified things so much with our wonderful food labels."

It's a sad fact that many people with diabetes are not highly motivated to control the disease. Still, you don't have to be pregnant to be motivated. If you count yourself as a part of this high achieving group—and that obviously includes many readers of this publication—the glycemic index may very well be worth investigating further. 

Glycemic Index List

By David Mendosa

Here are some of the most important of the 300 or so foods for which scientists have determined their glycemic indexes. The higher the index of a food the quicker it raises blood sugar.

The index uses white bread as the baseline with its index set as being equal to 100. Another index sets glucose as equal to 100. To convert to that list multiply the index number here by 0.7.

Food                                  Index
Yogurt, low fat, artifically sweetened  20
Soy beans                               25
Rice Bran                               27
Cherries                                32
Fructose                                32
Peas, dried                             32
Barley, pearled                         36
Grapefruit                              36
Milk, full fat                          39
Kidney beans                            42
Black beans                             43
Apricots, dried                         44
Milk, skim                              46
Lima beans, baby, frozen                46
Fettuccine                              46
Chick peas (garbanzo beans)             47
Pear, fresh                             53
Spaghetti, wholemeal                    53
Apple                                   54
Navy beans                              54
Plum                                    55
Pinto beans                             55
Apple juice                             58
Black-eyed beans                        59
Kelloggs' All-bran                      60
Peach, fresh                            60
Orange                                  63
Macaroni                                64
Linguine                                65
Lactose                                 65
Grapes                                  66
Pineapple juice                         66
Rice, parboiled                         68
Peas, green                             68
Grapefruit juice                        69
Carrots                                 70
Pumpernickel                            71
Ice cream, low fat                      71
Orange juice                            74
Special K                               77
Banana                                  77
Sweet potato                            77
Oat Bran                                78
Buckwheat                               78
Sweet corn                              78
Rice, brown                             79
Popcorn                                 79
Apricots, fresh                         82
Honey                                   83
Rice, white                             83
Split pea soup                          86
Oatmeal                                 87
Ice cream                               87
Raisins                                 91
Beets                                   91
Sucrose (table sugar)                   92
Pineapple                               94
Grapenuts                               96
Stoned Wheat Thins                      96
Cornmeal                                98
Wheat bread, wholemeal flour            99
Shredded Wheat                          99
Melba toast                            100
Cream of Wheat                         100
Millet                                 101
Wheat bread, white                     101
Bagel, white                           103
Watermelon                             103
Swede (rutabaga)                       103
Cheerios                               106
French fries                           107
Donut                                  108
Waffles                                109
Total                                  109
Broad beans (fava beans)               113
Pretzels                               116
Rice Krispies                          117
Cornflakes                             119
Potato, baked                          121
Glucose                                137
Parsnips                               139
Dates                                  141
Glucose tablets                        146
Maltose                                150

Source: Jennie Brand-Miller et al., The Glucose Revolution: The Authoritative Guide to The Glycemic Index, The Groundbreaking Medical Discovery (New York: Marlowe & Company, in press).

This article originally appeared in Diabetes Wellness Letter, July 1999, pages 3-5.

Last modified: January 12, 2001

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