I was searching some tips and found the following web article. Hope it may be useful to some of you.
I remember how my mom constantly scolded my dad for all those "unhealthy" diet and habits, so I know that will never work. (Unfortunately my dad passed away at 62 with cancer, yet kids won't really grow up healthy with a nervous mom, regardless how many healthy rules she imposed)
I found that I have to restrain such impulse to repeat the same words every time I see a dear friend doing something unhealthy. I don't want to be a health freak. I know how stubborn friends get even more stubborn if you overdo your suggestion. They feel like you're stepping their feet when you try to "tell" them something.
So recently I was aware of such challenge and tried to be "creative" and "moderate:"
1. Give a very simple, straight forward tip that your friend will be able to try immediately. Or just remind him something that has worked before.
2. Limit to 1 tip/question per 3 days.
3. Just ask "how do you feel yesterday" next time and see if your friend tried it or not. Just listen. If he think it's getting better, he may not want to deal with it anymore.
4. If your friend are kind to skeptical, pretend it's not your idea, you heard it from somewhere/someone else, a real story that is more convincing.
5. If things don't work. Just show that you're sorry to see them feel bad.
6. "Just let me know if you need anything" or "I wish you get better so we can go for a vacation" will be much effective than "you should quit ice cream."
7. Post a relative web article link on your Facebook or personal blog if he's following. Or ask other friends to post it on theirs.
8. I recall a quote from solution focused therapy, "Never work harder than your client."