This claim that soy foods prevent heart disease is based on the fact that soy foods lower cholesterol. Soy foods can lower cholesterol, however this is not necessarily a good thing. Lowering cholesterol does not prevent heart disease like we used to think, and can, in fact cause an increase in other disorders including cancer, autoimmune disorders, intestinal diseases, stroke, accidents, violent behavior, depression and suicide.
Source:No Joy in Soy