Recent things I've heard/read:
Fruit has too much sugar and is bad for your teeth.
Carbs make you fat.
High fat content makes you fat.
Meat is full of antibiotics etc and you can't be sure where it's come from (like in the horsemeat scandal!)
Potatoes are dodgy because if they have any green on them they have begun to secrete a poisonous chemical.
Rice contains arsenic.
Oily fish contain pollutants and some fish contain high levels of mercury.
Vegetables are sprayed with chemicals.
etc
etc
Some of the above are true, some I'd question. Most are only an issue if you eat a large amount of that thing. All things in moderation is my motto - otherwise you'd starve!