How do you make people change their behaviour and do something they might find boring or hard? By making it FUN. This video shows how you can attract people to use their seatbelts by rewarding them for doing so:
What is harder though, is to make people STOP doing something. Advertising and marketing is most times about convincing people to ADD on things to their lives, which is easier than convincing people to remove something, because the brain gets attached as soon as it has got it´s hand on something. Once you own it, you value it higher. Once it´s yours, you will defend it.
So how do you make people STOP eating junk? The easiest way is to turn it all around and make them START doing something else. ADD instead of REMOVE. If you want people to stop drinking, make sure you tell them what you will replace this treat with.
This makes it more positive, and we all prefer sunshine before rain.