Ever wonder why what is good for you today according to the latest study is what is bad for you according to tomorrow's study? Well, now we know:

http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.0020124

This may be a bit technical for some of you but pretty much what it says that if you do enough studies you are going to find contradictory results, particularly when the thing being studied is complex (like the human body for example).