I've done some research on soya. I am in the process of putting it all together with references etc, but it's not ready yet (as you know if you've searched about a bit there's a LOT of studies out there to compare, source etc).
I'll give you the basic outline for now & anything else you will have to wait until I've finished compilling (sorry mate
First off before we start you need to know about the soya, meat/dairy war that's been raging for some time now. Various studies are published by either the soya industry (soya is the stuff of heaven & can cure everything from cancer to the common cold) & the meat/dairy industry (any man touching soya will grow breasts). Some of the "so called" research coming out has been of the lowest quality around & any sort of peer-review could/should tear it apart (doesn't happen so much these days as those doing the peer-reviewing know their next job is probably coming from the same guys who funding the research before them).
So you have to bear these facts in mind when reading research. Don't just hop to the conclusions, check how they prepared any study, see what results they've got to get their conclusions (you'd be surprised how many studies get one answer, but have an opposite conclusion!).
Now, here's the facts about soya. Soya has products called phyto-oestrogen in them. They are called phyto-oestrogens because they have a similar make-up to the estrogens in animals. They are said to be about 5,000 times less potent than oestrogen from animals (I've seen other figures for this, it depends upon which type of test you do, but at minimum it's 100's of times less potent by any standard).
Here's the theory (NOT fact): There are two camps of thought. It could be that phyto-oestrogens can fit into the receptors designed for endogenic oestrogen (produced within the organism) - this is by no means proved, but if it can then it could have one of several effects:
a/ It blocks the receptor from any endogenic oestrogen, so would have an anti-oestrogen effect.
b/ As it acts like a very weak oestrogen it blocks the receptor from an endogenic oestrogen, so by acting much more weakly than the endogenic oestrogen acts as an anti-oestrogen (you get a weaker effect than an endogenic oestrogen, so in effect it acts like a block)
c/ It fits into a receptor & acts like oestrogen
At the moment the majority of research supports either a or b. There have been some feminising effects from some research, but this has been from purifying huge amounts of phyto-oestrogen & force-feeding it to rats (who, by the way, metabolise differently to humans), but more realistic studies have shown mainly no or a very slight anti-oestrogenic effects.
As a side note, in studies of soya Vs whey there was no difference in effects of hypertrophy.
I'd like to move back a step here & ask a question. Does ingesting oestrogen have an effect upon the hormonal make-up of the body to any great extent. Firstly any hormone is made of amino acids, now one thing the body is good at is getting at amino acids, breaking them down & assimilating them (there are the odd exceptions to this with prions etc, but as a rule stomach acid does a good job of breaking down any amino acid groups to their base components), but for now assume that oestrogen can make it into the body in reasonable amounts. Now, how do you think the effect of drinking the blood products of a lactating mother would effect your oestrogen levels? Milk products are swimming in oestrogens & yet they've never been associated with the feminising of males. As milk is fed to all growing males it would infact be implied that to keep our "maleness" we've had to have some system to protect ourselves from any potential feminising effects that we'd recieve the first few years of our lives. You cannot say that the very weak effects of phyto-oestrogen have this massive effect upon the males producing breasts etc & yet that the consumption of milk (& milk products, including whey) do not have any effect, unless you're claiming that oestrogen for mammals is broken down in the stomach, but phyto-oestrogen is not (but this would imply that phyto-oestrogens are very different from mammal oestrogen, so almost certainly wouldn't work in the same fashion within the body?).
So, as you can see the "feminising effects" of soya is propoganda, or misunderstood research or terms.
Another point is most plant based foods contains phyto-oestrogens (which are chemicals that look slightly similar to our oestrogen, but serve a totally different function within the plant), so you'd probably have to avoid plant food to avoid phyto-oestrogens
OK, I think that's enough for now except to say that I'd take the middle ground with soya. I don't believe the "wonder food" hype it's being given, nor do I believe to "food from hell" hype that being pumped out. Treat soya like any other food. One that's got a decent amount of protein, for sure, but one that's not the "cure-all" either.
Having soya will not cause breasts anymore than having whey will.