It’s been a while since I graduated but I think it was something like that: there is a molecule in soy that can be metabolized and then binds to estrogen receptors. However, there are two different receptors that, when activated, will have different signaling cascades and effects. That soy molecule binds to one of them. But only about 50% of people (I think the study was done in menopausal women) metabolize that molecule to the active, estrogen-receptor binding molecule. The others don’t and soy has absolutely no effect on them. For those who do metabolize it, it can have an effect on some estrogen-regulated pathways, but it is not “estrogen” and cannot substitute it.