The glycemic index is a measure of the rate at which a carbohydrate raises blood glucose levels after ingestion. With use of the glycemic index method, foods that contain carbohydrates get a rating from zero to 100. The rating for each food is relative to the rating for glucose itself, which is 100. Carbohydrates with a high glycemic index, 70 or above, produce a large and abrupt increase in blood glucose and insulin levels. Carbohydrates with a low glycemic index, 55 or below, raise blood glucose and insulin levels slowly after consumption.
Significance of the Glycemic Index
The glycemic index method of classifying carbohydrates has its roots in the development of diets designed to help diabetics control their blood glucose levels. Over the last 20 years, the glycemic index has taken on a more wide-ranging role as a tool used by doctors in Canada, Australia and Europe as part of nutritional therapy for their patients. A diet that features carbohydrates with a low glycemic index may help lower the risk of such medical problems as cardiovascular disease, diabetes and obesity, according to the Florida State University Department of Health Promotion and Nutrition Services.
Examples of Specific Foods
The American Diabetes Association lists carbohydrate-based foods that have high, medium and low glycemic indexes. High glycemic index carbohydrates include white bread or bagels, corn flakes or bran flakes, pretzels, popcorn, short grain white rice, russet potatoes and saltine crackers. Carbohydrates with a medium glycemic index include brown or wild rice and rye and pita bread. Examples of low glycemic index carbohydrates include pumpernickel bread, rolled or steel-cut oatmeal, oat bran, barley, sweet potatoes, pasta, converted rice and most fruits. Low glycemic index carbohydrates have the highest health and nutritional value because they help keep blood sugar and insulin levels low and provide long-lasting energy.
Method of Determining Glycemic Index
Scientists use volunteers to determine the glycemic index of a food. On one day, the volunteers consume a test food that contains 50 g of available carbohydrate; blood sugar levels are measured before consumption and at regular time periods for several hours afterward. On another day, the volunteers consume 50 g of glucose as a control, and blood sugar levels are measured as they were for the test food. To calculate the glycemic index, scientists divide the blood sugar response to the test food by the response to the glucose control and then multiply by 100.
Benefits of Low Glycemic Index Carbohydrates
ScienceDaily.com summarizes an article in the July 2006 issue of "Archives of Internal Medicine" in which researchers described the results of a randomized, controlled clinical trial that compared high and low glycemic index diets. They found that a diet based on low glycemic index carbohydrates and high protein was an effective way to lower the risk of cardiovascular disease. In addition, the "Los Angeles Times" reported on a research paper in the December 2008 issue of "Journal of the American Medical Association" in which scientists found type 2 diabetes patients on a low glycemic index diet had better blood glucose control and bigger improvements in cholesterol levels relative to patients on a high-fiber diet.
References
- Florida State University Department of Health Promotion and Nutrition Services: Glycemic Index
- American Diabetes Association: The Glycemic Index of Foods
- Oregon State University: Linus Pauling Institute: Measuring the Glycemic Index of Foods
- ScienceDaily.com: Low Glycemic Index Diet Best for Weight Loss and Cardiovascular Health
- "Los Angeles Times": Low-Glycemic Diet Best for Diabetics, Study Shows
