I think I'd want to keep the change subtle. No matter how well intentioned, abrupt, sweeping, global change can have unintended consequences. I'd want people to be slightly less self involved, or at least more cognizant of how their behavior affects others. Maybe this small change will lead to people working together to actually solve the various issues we seem to have as a society, rather than using those issues to prop up our own respective agendas...

That, or I would make it so that a bowl of ice cream provided the same health benefits as a bowl of raw vegetables.