My motherinlaw is japanese and eats natto to keep her blood pressure down is this possible? Its fermented soybeans how could this help she eats 1xday

It is possible. It is possible. Nattō is made from soybeans fermented with a bacteria called bacillus subtilis. This bacteria produces an enzyme called nattokinase, which has effects similar to a class of drugs called ace inhibitors, which are used to treat high blood pressure.
It does! Eating a fermented soybean product called 'natto, ' has been researched and shown to mildly lower blood pressure. However, it's principle benefit is to lower clotibility of blood. It is a food used for nutritional support in japan, dating back to feudal times in that country. It may help lower heart disease by several mechanisms.