Glycemic Index Diet Emphasizes ‘Good Carbs'
WebMD Health News
Reviewed By Elizabeth Klodas, MD, FACC
Latest Diabetes News
Dec. 16, 2008 -- Following a diet designed to keep blood sugar from rising after meals helped diabetic people keep their disease under control in a new study published in the latest Journal of the American Medical Association.
People with type 2 diabetes who ate what is known as a low-glycemic-index diet for six months had greater blood sugar control and fewer heart disease risk factors than those who followed another eating plan.
Both diets were high in fiber and low in saturated fat, and both derived about 40% of their calories from carbohydrates.
But the low-glycemic-index diet emphasized carbohydrates that had less impact on blood sugar levels, such as beans, pasta, nuts, and certain whole grains.
"These are the basic foods that your grandparents probably ate but they are no longer staples of the American diet," lead author David Jenkins, MD, of Toronto's St. Michael's Hospital and the University of Toronto, tells WebMD.
What Is a Low-Glycemic-Index Diet?
The basic premise behind the low-glycemic-index diet is that all carbs are not created equal.
Some cause big spikes in blood sugar and others have little impact on blood sugar levels.
Specifically, the glycemic index measures how much a 50-gram portion of a carbohydrate raises blood sugar levels compared to pure glucose, which has a glycemic index score of 100.
Typically, foods that score higher than 70 are considered high-glycemic-index (GI) foods; those that score 55 and under are considered low-GI foods.
Many highly refined foods, including white bread, corn flakes, and instant potatoes have high GI scores; unprocessed, high-fiber foods tend to have lower GI scores.
But it isn't as simple as saying choose unprocessed high-fiber foods.
- Foods such as carrots and potatoes can either be high-GI or low-GI foods, depending on several factors, including how long they are stored and how they are cooked or processed.
- Pasta that is cooked al dente has a lower score than pasta that is cooked longer. Rice can range from a low of 55 to more than 100, depending on variety and cooking time. The same is true with potatoes. And the riper the fruit or vegetable, the higher the score.
- Research suggests that the GI response to a given food also varies from person to person and can even vary within the same person from day to day.
- Some highly processed foods like cola and even some candy bars score low. A Snicker's bar, for example, has a GI score of about 55.
"We don't think of cola and Snicker's bars as health food, even though they are relatively low-glycemic-index foods," American Diabetes Association President of Medical Science John Buse, MD, PhD, tells WebMD. "If the diets of the people in the study included a lot of unhealthy, low-glycemic-index foods, I don't think they would have gotten the benefits they did."
Good Carbs, Bad Carbs
The low-glycemic-index dieters in the study ate plenty of legumes, peas, lentils, nuts, barley, oatmeal, pasta, and rice that were boiled briefly. They also ate low-glycemic-index breads, including pumpernickel, rye, and breads made with quinoa and flaxseed.
The foods were also paired with an eye toward keeping the post-meal blood sugar spike low. Pasta was often served with legumes, for example.
The other group of dieters ate more traditional carbohydrates including whole-grain breads and breakfast cereals, brown rice, and potatoes with skins on.
- Both groups of dieters limited saturated fats, trans fats, and white flour.
- They were told to avoid pancakes, muffins, doughnuts, white bread, bagels, rolls, cookies, cakes, popcorn, french fries, and chips.
- Both groups also ate five servings of vegetables and three servings of fruit a day, but the low-GI dieters avoided tropically grown fruits like mangos, bananas, and pineapple, which tend to have higher GI scores.
The 210 study participants were all taking drugs to control their diabetes and most were overweight or obese.
At the end of six months, both groups had lost about the same amount of weight. But the low-glycemic-index dieters saw more improvement in blood sugar control and heart disease risk factors than the other dieters.
Jenkins acknowledges that the difference was modest, but he adds that the findings show that the low-glycemic-index diet can help diabetic people who are highly motivated.
"This diet is not a diet for everyone, but for the person who is motivated to keep their diabetes under control, this is a good strategy," Jenkins says.
Nutrition educator Emmy Suhl of Boston's Joslin Diabetes Center agrees, but she says getting most people with type 2 diabetes to stick to a low-glycemic-index diet would be difficult.
"Diabetes is epidemic and this is a low-cost approach to treating it," she tells WebMD. "The improvement they saw (in blood sugar control) was not that great, but every little bit helps. And this had the added benefit of having some reduction in cardiac risk factors."
SOURCES: Jenkins, D.A., The Journal of the American Medical Association, Dec. 17, 2008; vol 300: pp 2742-2753. David A. Jenkins, MD, St. Michael's Hospital; professor of nutritional sciences, University of Toronto. John Buse, MD, PhD, president, medicine and sciences, American Diabetes Association; director, Diabetes Care Center; chief, Division of General Medicine and Clinical Epidemiology, University of North Carolina School of Medicine, Chapel Hill, N.C. WebMD Expert Review: "The Glycemic Index Diet (Low Glycemic Diet)." Emmy Suhl, registered dietitian, Joslin Diabetes Center, Harvard Medical School, Boston.
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