Some say soy increases estrogen levels, although I have never seen a study to 100% back this claim.

I heard that too and seen stuff about it.. in this case i don't need soy so i wont try it.

It does not increase estrogen. It contains substances called phytoestrogens, these are plant substances that fit onto some (not all) estrogen receptors). It has long been speculated that because of this, soy products might help relieve the symptoms women experience during menopause and thus be an alternative to hormone replacement therapy.

However recent research has shown this is not the case.

Ive gotta say I don't believe that id does decrease it myself and frequently drink cartons of Soy Slender chocolate unsweetened soy milk. Amazing stuff, still not so much of a tofu person though.