Soy consumption and incidence of gestational diabetes mellitus: the Japan Environment and Children’s Study

Background: Intervention studies have shown that isoflavone treatment improved glucose metabolism, indicating that soy intake may have a potential role in diabetes prevention. Objectives: We aimed to investigate the prospective association of soy isoflavone and soy food intakes with incidence of gestational diabetes mellitus (GDM) in a birth cohort study. Methods: We recruited 97,454 pregnant women (median gestational age 12 weeks) between January 2011 and March 2014. Dietary intakes during the 12 months preceding study enrollment were assessed by a semi-quantitative food frequency questionnaire. The relative risks of GDM associated with soy isoflavone and soy food intakes were obtained by Poisson regression. Demographic information, histories of diseases, socioeconomic status, lifestyles, and dietary habits, obtained by a self-administrated questionnaire, were used for covariate adjustments. Results: We identified 1904 cases of GDM (2.2%) among 84,948 women. Compared with those in the lowest quintile of soy isoflavone intake, women in the highest quintile were found to have experienced a significantly lower risk of GDM (multivariate relative risk = 0.82; 95% confidence interval: 0.70, 0.95; P for trend = 0.05). Similar results were observed for genistein and daidzein. Regarding soy foods, intakes of miso soup and natto were inversely associated with GDM incidence (both P for trend ≤ 0.01), whereas the association for tofu intake appeared to be nonlinear (P for trend = 0.74). Conclusions: Higher intakes of miso soup and natto before and during early pregnancy, compared with lower intakes, may be associated with a lower incidence of GDM.