Should there be a fat tax?

As a smoker, I have to pay a lot more tax than a non-smoker because I supposedly cost the system more (some people's rationale). If that's true, then why is there no fat tax? Once you've hit 5'8" and 350lbs you're definitely going to be a burden on either the hospitals, social workers, welfare or all three. Why should I have to pay higher tax when I do not burden such systems and will die rather quickly and cheaply from lung cancer and not even collect a pension?