As you see it's about the binding affinity, even E2 has a very poor binding ability. But, you don't won't to push ER-a too much because of the proliferation of breast cancer. A balanced approach would be much safer. And incidentally, (CLA)-conjugated linolelic acid protects against breast cancer.

Conjugated linoleic acid induces apoptosis through estrogen
http://www.biomedcentral.com/1471-2407/8/208