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

Background: Evidence regarding the consumption of soy foods and isoflavones in relation to risk of type 2 diabetes (T2D) is scarce. Objective: Our study was to evaluate the association between soy food and isoflavone consumption and risk of T2D in US men and women. 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 y. Self-reports of incident T2D was confirmed by a validated supplementary questionnaire. Results: During 1,966,321 person-years of follow-up, 9,185 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 to non-consumers of soy foods, the hazard ratio (HR) was 1.00 (95% 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.