You have a friend who is trying to lose weight. This friend believes that taking up smoking will help with weight loss. What advice would you give to your friend? What other options does your friend have for weight loss? Do you think smoking can really help a person to lose weight?
Honestly, try to guide them towards doctor approved ways. If they don't listen, then don't push it, though, or they'll push you away. Try to be there for them at least.