Association of Soy and Fermented Soy Product Intake with Total and Cause-Specific Mortality

Japan Public Health Center study following nearly 93,000 adults examined whether the type of soy product consumed — fermented or not — influenced all-cause and cardiovascular mortality.

Total soy intake showed no significant association with death. But fermented soy, particularly natto, told a different story: higher consumption was significantly associated with lower cardiovascular mortality. The effect was specific to the fermented fraction, not soy writ large.

The finding matters because natto is fermented with Bacillus subtilis and contains vitamin K2 as MK-7, nattokinase, and other bioactive compounds absent from tofu or soymilk. Isolating the fermented signal from total soy intake is methodologically important — and this study did it in a large, representative Japanese population.

The limitation is the observational design in a homogeneous cohort. Fermented soy consumption correlates with traditional dietary patterns and lifestyle, making confounding difficult to eliminate entirely. The finding requires experimental confirmation before dietary recommendations can follow from it.

We rate the evidence moderate. A large BMJ-published cohort adds meaningful weight to fermented soy as a potentially beneficial dietary pattern for cardiovascular mortality — the specific association with fermented products, not soy generally, is the most interesting signal.