Phytoestrogens (the ones found in soy beans) have nothing to do with the human hormone estrogen other than the name (and how they look in a chemical context). They do not have any measurable impact on your hormonal makeup and this bodybuilding myth has been disproven dozens of not hundreds of times.

You know what contains actual mammal estrogen? Beef and milk from cows that have been given hormones to give more milk.