Governments have very effectively reduced tobacco use through advertising, restrictions on where smoking is legal (backed by force), and taxation (backed by force). Making something expensive and inconvient can make it unpopular while avoiding potentially counterproductive bans. The same principles could be applied to unnaturally delicious processed foods.
I would hazard a guess that the decline in celebrity endorsement of tobacco products had a larger influence on the total decline of smoking at least in the adult population. Mind you, this wasn't uniform as the rate of smoking has not declined at the same rate for poorer populations despite the absence of both advertisements or celebrity endorsements.
