I think the government realises we're getting fatter, and things like a sugar tax (like the cigarette tax) are designed to profit off of this fact.
Lectraplayer, that's a nice sounding idea too. How would you implement something like that? It's a lot harder to make nice-sounding advertisements, since a lot of traditional techniques for getting people to buy things were guilt tripping them into believing that their lives would be better with them. I'm not really sure how an advert encouraging exercise that doesn't diss being overweight would play out.
Here in Australia, we've got a bunch of TV adverts and billboards from this company called LiveLighter. I don't know if it's government sponsored or whatever, but it's trying to scare us away from extra sodas and extra food in general through showing
~toxic fat around your vital organs.~ They can get away with showing guts and gore stuff on prime time TV and huge billboards (like at the train station in the city) in the name of scaring us healthy.
Here's a link to their list of advertisements. They're just gross all round.