High glycemic index diet may boost diabetes risk

NEW YORK (Reuters Health) - Regular consumption of foods with a high glycemic index appears to increase the risk of type 2 diabetes in African-American and Chinese women, according to the results of two studies published Monday.

Glycemic index refers to how rapidly a food causes blood sugar to rise. High-glycemic index foods, like white bread and potatoes, tend to spur a quick surge in blood sugar, while low-glycemic index foods, such as lentils, soybeans, yogurt and many high-fiber grains, create a more gradual increase in blood sugar.

For their study, Dr. Supriya Krishnan, from Boston University School of Public Health, and colleagues examined data from 40,078 U.S. black women who filled out a food questionnaire in 1995. The glycemic index and glycemic load were calculated. Every two years through 2003, the women provided up-to-date information about their weight, health and other factors.

During 8 years of follow-up, 1,938 women developed diabetes. Results showed that women who ate high-glycemic index foods or a diet with a high glycemic load had a higher risk for diabetes. However, women who ate more fiber from grains (cereal fiber) had a reduced risk.

"Our results indicate that black women can reduce their risk of diabetes by eating a diet that is high in cereal fiber," Krishnan and colleagues write. "Incorporating fiber sources into the diet is relatively easy: a simple change from white bread (two slices provides 1.2 grams of fiber) to whole wheat bread (two slices provides 3.8 grams of fiber) or substituting a cup of raisin bran (5 to 8 grams of fiber) or oatmeal (4 grams of fiber) for a cup of corn chex (0.5 grams of fiber) or rice chex (0.3 grams of fiber) will move a person from a low fiber intake category to a moderate intake category, with a corresponding 10 percent reduction in risk."

In the other study, Dr. Raquel Villegas, from Vanderbilt University Medical Center in Nashville, Tennessee, and colleagues followed a group of 64,227 Chinese women for an average of five years. They interviewed the women every two years between 2000 and 2004, to gather health-related information such as dietary habits and physical activity levels.

During follow-up, 1,608 women developed type 2 diabetes. Results showed that women who consumed more carbohydrates overall were more likely to develop diabetes. When they were split into five groups based on carbohydrate intake, those in the group consuming the most (about 337.6 grams per day) had a 28 percent higher risk than those in the group consuming the least (about 263.5 grams per day).

Women who had diets with a higher glycemic index and who ate more staples such as bread, noodles and rice specifically also had an increased risk. Women who ate 300 grams or more of rice per day were 78 percent more likely to develop diabetes than those who ate less than 200 grams per day.

"Given that a large part of the world's population consumes rice and carbohydrates as the mainstay of their diets, these prospective data linking intake of refined carbohydrates to increased risk of type 2 diabetes mellitus may have substantial implications for public health," Villegas' team concludes.

SOURCE: Archives of Internal Medicine, November 26, 2007.