1) I think it is covered under, "Everything is permitted but not everything is beneficial". We should take care of our bodies as well as we can--that we owe it, out of gratitude, to the One who created it. 2) I have often seen 1 Corinthians 3:17 quoted in regard to smoking but I really don't think that is the theme of 1 Cor. 3. I believe that passage is referring to the Body of Christ when it speaks of the "temple of the Holy Spirit". We have no need of the Jerusalem Temple now because the Church is still here for the people of God. 3) All that is to say that, while smoking is not very wise--knowing what we do about its disease-causing properties--it is still not something that we should get legalistic about. C.S. Lewis liked to smoke a pipe and sip a bit of brandy in the evening. We are saved by our faith not by our behavior. 4) We are ALL dying every day of our lives. Some things we do probably hasten our death. Eating too much and eating junk food is a "sin" that no one in the churches speaks much about--but may be as death-promoting as smoking--considering the Type II diabetes epidemic, which definitely shortens the lifespan. 5) Other health-promoting habits can possibly forestall death. But, since Paul told us that "to die is to gain" why should we worry like the health-obsessed crowd does? Believe me, I have seen people do bizarre things in order to live longer--or so they think. (Coffee enemas?? Gross.). A doughnut would never cross their lips, and they spend two hours at the gym every day. But, in the end, they will die too. We who are children of God have the assurance that we will be going on to something infinitely better than this life.
6)"It was for freedom that Christ set us free." Don't let anyone take your freedom away by trying to shame you. If you quit smoking, or eating junk food, do it to please Him.