A special tax on fatty or otherways unhealthy food isn't and shouldn't be the answer.
Proper labeling of food, including fast food, would be a better choice.
Having a caloric breakdown in type large enough for people to actualy read and printed on all fast food wrappers or containers would go a long way towards helping people make the right choice.
As it is now, trying to figure out that that Whopper with cheese has 850 calories, about 450 from fat, and the bun has about 50 grams of carbohydrates of which only 5 are fiber, isn't very easy.
Sure, they'll post a placard with those numbers but there's a disconnect when the info on that placard isn't on the food wrapper itself.
I'm all for personal choice but I also believe that the public needs to have this info available on the product they're buying to make that informed choice.