Consumption of soy foods and isoflavones and risk of type 2 diabetes: a pooled analysis of three US cohorts

BACKGROUND/OBJECTIVES: Evidence regarding the consumption of soy foods and isoflavones in relation to risk of type 2 diabetes (T2D) is scarce. Our study was to evaluate the association between soy food and isoflavone consumption and risk of T2D in US men and women. SUBJECTS/METHODS: We followed 63 115 women in the Nurses' Health Study (1998-2012), 79 061 women in the Nurses' Health Study II (1999-2013) and 21 281 men in the Health Professionals Follow-Up Study (2002-2010). Diet was assessed by a validated food-frequency questionnaire and was updated every 4 years. Self-reports of incident T2D were confirmed by a validated supplementary questionnaire. RESULTS: During 1 966 321 person-years of follow-up, 9185 incident T2D cases were documented. After multivariate adjustment for covariates, consumption of soy foods (tofu and soy milk) was not associated with a lower T2D risk. Compared with non consumers of soy foods, the hazard ratio (HR) was 1.00 (95% confidence interval (CI): 0.93, 1.07) for < 1 serving/week and 0.93 (95% CI: 0.83, 1.03) for >= 1 serving/week of soy foods (P for trend = 0.14). In contrast, intake of total isoflavones was inversely associated with T2D risk. Comparing extreme quintiles of isoflavones, the HR was 0.89 (95% CI: 0.83, 0.96; P for trend = 0.009). Inverse associations were also found for consumption of major individual isoflavones, including daidzein and genistein, with risk of T2D. CONCLUSIONS: Intake of isoflavones was associated with a modestly lower T2D risk in US men and women who typically consumed low-to-moderate amounts of soy foods. These findings warrant replications in other populations with similar soy intake levels.