December 4, 2007 — High intake of foods with a high glycemic index (GI), especially rice, may increase the risk for type 2 diabetes mellitus in middle-aged women of Chinese descent, according to the results of a large prospective study in the November 26 issue of the Archives of Internal Medicine.

"Much uncertainty exists about the role of dietary glycemic index and glycemic load [GL] in the development of type 2 diabetes mellitus, especially in populations that traditionally subsist on a diet high in carbohydrates," write Raquel Villegas, PhD, from the Vanderbilt University Medical Center in Nashville, Tennessee, and colleagues. "Using data collected in the Shanghai Women's Health Study, we prospectively examined the relationships between dietary carbohydrates, GI, GL, and carbohydrate-rich foods with the risk of type 2 DM [diabetes mellitus] in middle-aged Chinese women."

The investigators observed a cohort of 64,227 Chinese women free of diabetes or other chronic disease at baseline for 4.6 years, using in-person interviews and a validated questionnaire to collect data on dietary habits, physical activity, and other pertinent information. Cox proportional hazards models were used to determine associations between dietary carbohydrate intake, GI, and GL and the incidence of diabetes.

During 297,755 person-years of follow-up, 1608 incident cases of type 2 diabetes mellitus were identified. Dietary carbohydrate and rice consumption were each positively associated with the risk of developing type 2 diabetes mellitus. For the highest vs the lowest quintiles of intake, the multivariable-adjusted estimates of relative risk (RR) were 1.28 (95% confidence interval [CI], 1.09 - 1.50) for carbohydrates and 1.78 (95% CI, 1.48 - 2.15) for rice. For increasing quintiles of intake, the RR was 1.00, 1.04, 1.02, 1.09, and 1.21 (95% CI, 1.03 - 1.43) for dietary GI and 1.00, 1.06, 0.97, 1.23, and 1.34 (95% CI, 1.13 - 1.58) for dietary GL.
 

"High intake of foods with a high glycemic index and glycemic load, especially rice, the main carbohydrate-contributing food in this population, may increase the risk of type 2 diabetes mellitus in Chinese women," the study authors write.

Limitations of the study include limited follow-up and statistical power, so that results of most of the tests for multiplicative interaction were not significant.

"In this large population-based cohort study, we found that a diet high in carbohydrates and with a high GI was associated with a higher risk of type 2 DM, in particular in participants with high WHR [waist-hip ratio] and BMI [body mass index]," the study authors conclude. "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 DM may have substantial implications for public health."

The US Public Health Service, National Institutes of Health, supported this study. Two of the study authors have received funding. The remaining study authors have disclosed no relevant financial relationships.