I'm past the breast feeding years, but the wisdom a dozen or so years ago when I WAS breast feeding, was that poor nutrition on the mom's part, meant mom got poor nutrition. Baby gets along okay. The thinking being that baby gets whatever there is to be had FIRST, so mommy is getting nada if there isn't much there to begin with. Also, I heard things like calcium being leeched out of bones to provide for the baby (think future osteoporosis risk and dental health issues for mom). I don't know if those are backed up by current science, but that is where I would start my search, if you really want to look into it.