Purpose: To examine the association between soy products and their components, isoflavones and protein, and incident type 2 diabetes in a population with varied soy intake and high rates of diabetes.
Methods: We used data from the Singapore Chinese Health Study, including 43,176 Chinese men and women aged 45-74 years, free of chronic disease at baseline (1993-1998) and followed through 2004. Intake of individual soy items, total unsweetened soy, and soy components was assessed by food-frequency questionnaire and examined with type 2 diabetes risk using Cox regression.
Results: During an average follow-up of 5.7 years, 2,252 of the 43,176 participants included in the current analyses developed diabetes. After adjustment for potential confounders and BMI, consumption of unsweetened soy was inversely associated with diabetes risk. Hazard ratios (HRs) and 95% CI for diabetes across unsweetened soy intake categories (none, 1-4/month, 1-2/week, 3-4/week, ≥ 5/week) were: 1 (referent), 0.81 (0.67-0.97), 0.76 (0.63-0.91), 0.76 (0.63-0.92), and 0.72 (0.59-0.89), respectively (P (trend) = 0.015). Conversely, in multivariate models, consuming sweetened soybean drink was positively associated with diabetes risk. HRs for diabetes across soybean drink intake categories (none, 1-3/month, 1/week, ≥ 2/week) were: 1 (referent), 1.07 (0.95-1.20), 1.12 (1.00-1.26), and 1.13 (1.00-1.28), respectively (P (trend) = 0.03). Furthermore, after full adjustment, including adjustment for sweetened soy items, we observed a marginally significant inverse association between isoflavone intake and diabetes (HR for the fifth compared to the first quintile: 0.76; 95% CI: 0.58-1.00; P (trend) = 0.08).
Conclusions: The current findings support a protective role for unsweetened soy foods and isoflavones on risk of type 2 diabetes.