It would be up to the insurance company to verify that the insured didn't smoke, drink, or whatever else the parties had agreed to.
I would even be in favor of modeling health insurance on something like the car warranty model. Some car warranties require the owner to maintain the automobile at his own expense (e.g. regular oil changes) in order to receive warranty protection. Why can't insurance companies require the insured to engage in similar regular maintenance in order to remain covered?
This way the relatively inexpensive costs of things like eye exams, teeth cleanings, annual check-ups would be purchased in the marketplace rather than paid behind the scenes by the insurance company.
If the insurance companies don't pay for these regular maintenance activities then the insured might not do them on their own and risk more expensive problems later on. If the insurance companies continue to pay for these activities then there is no market pressure to lower cost and improve efficiency.
What do you think?