"It is true that cruciferous vegetables such as cabbage, kale, Brussels sprouts, broccoli and cauliflower contain natural chemicals called goitrogens (goiter producers) that can interfere with thyroid hormone synthesis. Other foods that contain these chemicals include corn, sweet potatoes, lima beans, turnips, peanuts, cassava (YUCA), canola oil and soybeans. Fortunately, the goitrogens in these foods are inactivated by cooking, even by light steaming, so there is no need to forego the valuable antioxidant and cancer- protective effects cruciferous vegetables afford."

http://www.drweil.com/drw/u/id/QAA355093

I would lay off soybeans and canola though (except for fermented soy products).  They are both dangerous for your health - regardless of what industry hype you may hear to the contrary.

DQ