Ration junk food in order to control peoples diets.
There's no real way to do anything to change the stats. Unless we can start patrolling the streets with whips encouraging the obese to run away from us.
The truth is, that a lot of people are more than happy to be overweight and obese. So long as they don't assault my ears with their winging about how they can't lose weight, when their going home indulging in cream cakes, then I say leave them to it.
If people want to lose weight, they will, they will put the effort in to be in a level of physical shape they're happy with and comfortable with.