Flaxseeds

 http://www.marksdailyapple.com/flax-prostate-cancer-risk/

Pros: 
omega 3 fatty acids, fiber, manganese
Cons: 
omega 3 fatty acids barely bioavailable by human body compared to those found in fish, high fiber can cause bloating, cyanogenic compounds in raw seeds, fats spoil quickly in ground seed, potential prostate cancer risk