Doesn't even have to be "better", just "different". The classic one is whether you should refrigerate eggs, which has diametrically opposite answers.

But anything that actually matters could be politicized at any time. I remember the John Gummer Burger Incident: http://news.bbc.co.uk/1/hi/uk/369625.stm , in the controversy over whether prion diseases in beef (BSE) were a problem.