By Sally Squires
Tuesday, January 15, 2008
In Australia, if you pick up a box of Lean Cuisine's chicken pomodoro you'll find a small blue and white symbol on the label that lists the product's glycemic index in addition to the usual facts about calories, carbohydrates, fat, protein and sodium. Some 150 other product carry the symbol, too.
Developed nearly 30 years ago at the University of Toronto, the glycemic index (GI) is becoming part of the nutritional landscape Down Under. And it's attracted attention here, too, among nutrition researchers and writers like me interested in understanding more about how our bodies process food.
The glycemic index tries to gauge how much your blood sugar is likely to rise after eating a particular food. The higher GI score of a food, the more it raises blood sugar -- something people, especially those with diabetes, need to avoid. Foods with scores of 70 to 100 are considered high-glycemic; those with scores of 55 or below are labeled low-glycemic.
In recent years, the glycemic index has been popularized by Jennie Brand-Miller, a professor of nutrition at the University of Sydney and the best-selling author of "The New Glucose Revolution" and 15 other books that collectively have sold more than 3 million copies. Brand-Miller says that eating according to the GI has numerous health benefits and is important both for those who have diabetes and for those who want to avoid it.
The widespread concept of the GI often gets boiled down to this: Skip foods with added sugar or processed white flour. But it's not that simple.
Take a potato. A hot baked potato has a glycemic index of nearly 90. But cool it in the refrigerator for a few hours and the starch is altered to a chemical form more resistant to digestion. That lowers the potato's GI score to about 56 when you reheat it or use it in potato salad.
or re-heat it. for other meals.
Food preparation also affects a food's GI score, as does ripeness. So a soft banana has a GI score of about 80, while a firm, slightly green banana has one of about 60.
"All of these issues makes the glycemic index sound too absurd and too complex and too variable to put into practice," Brand-Miller says. "But I don't think it is as hard as people imagine."
To help guide consumers, she has teamed with Diabetes Australia and the Juvenile Diabetes Foundation to form a nonprofit group that gives foods GI numbers and labels. Under the program, foods are tested and given a score. Lean Cuisine's chicken pomodoro gets a 47, Wonder's white low-GI bread, 54; and Nestle's all-natural 99 percent fat-free mango yogurt, 55.
In the United States, it's a different story: Only one food -- a sugar substitute extracted from cactus and marketed by Sweet Cactus Farms -- has undergone testing to get the blue GI symbol. And while a growing number of weight-loss books and cookbooks pay homage to the GI approach, neither the American Diabetes Association nor many U.S. nutrition experts have embraced its widespread use.
The glycemic index is "very useful in research," says Walter Willett, chairman of the Harvard School of Public Health's nutrition department, which developed the concept of the glycemic load, a companion measure based on the GI. "But I'm not in favor of putting it on food labels or of having people shop on the basis of GI numbers."
Two reports in this month's American Journal of Clinical Nutrition -- and two editorials on the findings -- cast some doubt on the usefulness of using the GI approach to control blood sugar or to cut the risk of heart disease and Type 2 diabetes.
In one study of nearly 2,000 adults ages 70 to 79, University of Maryland researcher Nadine R. Sahyoun and her colleagues found that a low-GI diet had no effect on participants' risk of developing Type 2 diabetes.
A year-long study by Thomas M.S. Wolever, a developer of the glycemic index at the University of Toronto, of people with Type 2 diabetes also found that the low-GI diet neither controlled blood sugar nor improved risk factors for heart disease any better than a high-GI diet or a low-carbohydrate approach.
"This is one of the longest studies examining the use of the glycemic index," says David M. Nathan, director of the diabetes center at Massachusetts General Hospital. "It is from the group that put the glycemic index on the map. It really shows no major benefit for weight loss or glucose control."
At the Mayo Clinic in Rochester, Minn., endocrinologist John Miles says, "I see a lot of patients eating sugar-free diets who also avoid starch but end up on high-fat diets. This does not make sense."
So Miles counsels his patients first to cut calories and fat to lose weight. "I am all for eating whole-grain bread," he says, "but if we allow our patients to put butter or a slice of cheddar cheese on it, they'd be better off eating Wonder Bread," which is a high-GI food.
Instead of eating by the GI numbers, many experts say it's simply better to eat plenty of fruit and vegetables, switch to whole grains and include small amounts of healthy fat in your diet.
Brand-Miller doesn't see it that way. "It helps a great deal for someone to adopt a diet based on whole grains, fruit and vegetables," she says. "But I think we can do better than that."