I have had breast cancer and heard you shouldn't drink soy milk. i drink one glass a day. is this ok?

No problem: Some chemicals in soy have estrogen-like properties. The amount of those chemicals is small. There is little hard data that soy is a risk, and it may be more like chemicals studied for preventing breast cancer. This article discusses that: j am coll nutr october 2001 vol. 20 no. Suppl 5 354s-362s.

Phytoestrogens: Can be components of some soy products, and if you had an er+ breast tumor, this *might* be a concern, but check with your oncologist...It is not clear that all soy milks have estrogenic activity or that they stimulate breast er+ tumors, in people, in mice, or even petri dishes.