Is obesity a choice or an addiction? Watch
There also are other factors at play that can cause obese people to struggle to change their lifestyle, but I'm not too well up on official definitions of addiction.
But OU Student is perfectly right, it's smacking of ignorance that implies the OP has not done his/her research into the topic - I for one know many who have gained weight as a result of medication, and been told "Stop eating more" when it has nothing to do with that.
Obesity isn't a choice, but of course it is a result of choices. The factors that influence us to make the choices we make, however, are usually more substantial than we tend to give credit for. It is well-known that 95% of diets fail (this, at least, is the figure apparently used by health professionals), and this should make us think carefully about how in control we really are. It is apparantly very difficult to lose weight and keep it off - it is not enough that we ask people to try harder, when will power itself is known to be a finite resource.
I would say that if you follow a certain course of conduct fully aware of the result, even if the result is not your desire or 'purpose' you have still chosen the result. It's called oblique intent.
They are not fully aware of the result, though. When considering to eat a burger, the person knows that whether or not they eat the burger or not will have no bearing on whether they will become obese. The problem is that of lifestyle, which is by no means a matter of simple choice.