It is always a very difficult situation to watch loved ones making choices that are not good for their health. It can be downright maddenening to see how they compromise their health, and it is even worse if you are a professional to whom others turn for advice in the very situation.
But just like the others already said: you cannot make choices for them. You can only lead a horse to the water but you cannot make it drink.
Continue to support the person, try not to enable bad habits, lead by example and don’t nag.