Telling an alcoholic to "stop drinking" is also completely useless advice. How many alcoholics do you think are like "Oh wow, you're right, if only I had known that all along..."
"You're overweight", says the Doctor, "you need to eat less and move more." "No s*t Sherlock with my IQ of 147 I'd never managed to put that one together myself," I replied.
There are definitely better ways to discuss the topic with someone you are trying to help.