http://search.orange.co.uk/redirect?...pdf%2Fsoya.pdf
the above is a pdf article that states how soya diet can affect your hormones -
it suggests that it may reduce follicle stimulating hormones and leutenising hormone both of which obviously go some way to reducing ovulation and develpoment of follicles
i cant give you advice but if i had pcos then i think i would give it a go.