I know it has to do with a phyto chemical that is destroyed during the fermentation process.
Heres some links (i just did as search on unfermented soy), its got lots of info, i didnt read it all just skimmed through.... though i question the one paragraph in the first link about protien, it claism that vegetarians cant get *omplete pretien" from veggies, well we all know this, but we als o know it doesnt have to be compelte, are bodies make about half of our amino acids while the other half must be obtained from food, so i am not sure how good this source is, since they are obviosly mis educated on protien and amino acids. anyway, that was kinda a rant....