Soy product and isoflavone intakes are associated with a lower risk of type 2 diabetes in overweight Japanese women.

Isoflavones have been shown to improve glucose metabolism, but epidemiologic data are limited. We prospectively investigated the relationship between soy product and isoflavone intake and the risk of developing type 2 diabetes among Japanese adults. Participants were 25,872 men and 33,919 women aged 45-75 y, who participated in the second survey of the Japan Public Health Center-Based Prospective Study and had no history of diabetes. Soy product and isoflavone intakes were ascertained using a 147-item FFQ. Odds ratios of self-reported, physician-diagnosed type 2 diabetes over 5 y were estimated using logistic regression analysis. A total of 1114 new cases of type 2 diabetes were self-reported. Intakes of soy products and isoflavones were not significantly associated with type 2 diabetes in either men or all women. However, among overweight women (BMI > or = 25 kg/m(2)), a higher intake of soy products was associated with a lower risk of type 2 diabetes; multivariable-adjusted odds ratios (95% CI) for the lowest through highest quintiles of soy product intake were 1.00 (reference), 0.78 (0.52-1.18), 0.79 (0.52-1.20), 0.62 (0.39-0.99), and 0.89 (0.55-1.44), respectively, and we found a similar risk pattern for daidzein and genistein intakes. Overall, our results suggest that there are no benefits of soy product or isoflavone intake with respect to risk of type 2 diabetes in either men or women. The possible protective associations of soy and isoflavone intakes among overweight women deserves further investigation.