I like to avoid synthesised/isolated forms of a compound, so after reading about natto and nattokinase here, I did a bit more looking into making it myself. I wanted to avoid high amounts of phytoestrogens too, so I looked for a bean that was reasonably low in phytoestrogens and widely available. I came up with mung beans. See the link below:Is anybody besides me worried about the fact that nattokinase, even though it dissolves blood clots is made of soy which is estrogenic? I guess there would be less soy in the nattokinase pills than eating the fresh natto which comes on cooked soybeans. Apparently serrapeptase also dissolves the fibrin in blood clots but has no soy….
Estrogen Foods List: 50 High Natural Phytoestrogen Sources – Superfoodly
List of the 50 foods highest in phytoestrogens to adapt or avoid in your diet. We breakdown how much isoflavones and lignans are in each.
superfoodly.com
While the research on mung bean natto is scarce, the little that does exist implies that it is just as good a source of both nattokinase and K2 as soy, if not marginally better. I've only made one batch so far. It worked out okay. I am assuming the stringyness of the beans is a proxy for how well the natto has formed. A little bit of experimentation will be required to optimize it.