>At least in the US where the problem is much worse than in the EU, I would say the major driving factor is the lack of cheap healthy foods.

And portion sizes! There a several factors that lead to such large portions. Americans expect (and now desire, thanks to the ever expanding gut lines) to be stuffed from an ordered meal so producers spend the extra $1 on food costs to ensure larger portions and fewer complaints. We'd complain is the the $9 burger was made into 1/3 sized $3 burgers. Additionally the fixed costs of running a food joint require to low cost and high margin items (like fountain soda) to survive.