Diet and Diabetes Risk in U.S. Black Women and Chinese Women: Glycemic Index and Load

The prevalence of type 2 diabetes has increased substantially in the U.S.; moreover, incidence rates are higher in some ethnic populations than in others (for example, black women are twice as likely as white women to develop the condition). Recent research has focused on modifiable risk factors such as dietary glycemic index (GI; a measure of the rapidity of carbohydrate absorption) and glycemic load (GL; a measure of the total glycemic effect of dietary carbohydrates). Eating high-GI foods triggers a rapid and sustained increase in blood glucose and insulin demand. In two studies, investigators examined the influence of GI, GL, and dietary carbohydrate sources on diabetes incidence in specific populations.

In the first study, U.S. researchers used a culturally sensitive food frequency questionnaire to assess cereal fiber intake, GL, and GI in 40,000 participants in the Black Women’s Health Study (age range at baseline, 21–69). During 8 years of follow-up, 1938 women were diagnosed with diabetes. In analysis adjusted for lifestyle factors (e.g., BMI, physical activity, and smoking), GI was associated with diabetes risk: The incidence rate ratio for women in the highest GI quintile compared with those in the lowest was 1.23 (95% confidence interval, 1.05–1.44). In contrast, women in the top quintile of cereal fiber intake had a lower risk for diabetes (IRR, 0.82; 95% CI, 0.70–0.96) than did those in the lowest quintile. The detrimental effect of higher GI and the protective effect of higher cereal fiber intake were most pronounced in women with BMI score <25.

The Shanghai Women’s Study included 64,000 China-dwelling women without baseline chronic disease (baseline age range, 40–70); 1608 developed diabetes during 5 years of follow-up. Diet was assessed at baseline and at 2-year follow-up. Of all foods consumed, rice contributed the highest dietary percentage (73.9%) to GL. In analysis adjusted for factors including age, smoking, physical activity, and BMI, both GI and GL were associated with risk for developing diabetes (relative risk of highest GI quintile vs. lowest, 1.21; 95% CI, 1.03–1.43; RR of highest GL quintile vs. lowest, 1.34; 95% CI, 1.13–1.58). The carbohydrate intake of these women far exceeded that of the primarily white women in previous large studies.