I've asked him many times if he has a life plan or goals but he only gets angry and doesn't answer me... but I did assume my responsibilities because I knew they were mine...
First of all, what makes you assume it's your responsibility? It's not your or anybody else's responsibility to change him. Actually no one is responsible for changing other people in this world. At his age, he is kinda immune to any "good" advice. He can change only when he realizes by himself and then he will decide to change. Otherwise even the enlightened being couldn't make him change.
Secondly, no one likes to be told what to do or what not, because chances are they know exactly that's what they should do. Especially in those rebellion ages. (You know what I am talking about.) Are there no ways to do something about it? Yes, there are ways, very subtle ways.
For example, instead of talking or advising or educating him, you can influence him by being a role model. But never ever show off. Otherwise it would disgust him. Do what you can do the best in your own life: eat well, study well, make good friends, etc. He will notice it, or probably he is watching you the whole time, who knows. And slowly he will be inspired to change his life too. But it's all up to him, no one else can change him but himself.
I believe that, intelligently he has no issue understanding what's best for him. Most of the time, it's all because of his old habits. Those habits keep propelling him to do those stupid things. How he formed those habits? That's another issue. But to get him out of his habits take enormous courage and self awareness. Still, it's not what you can do about it. It's up to him.
If you feel that you must do something, you could try reading some books, which are full of insightful and life touching stories, while he is eating. But, do not sit beside or in front of him to read. Sit behind him somewhere in a distance. Reading in a volume that he can hear you but don't read it aloud. When you read it, make sure you really enjoy reading it to yourself. (The worst practice would be, he thinks you are reading the books to him.) When he is eating, knowingly or unknowingly his whole system is in a relatively open state. That way something could subtly and magically happen to him. It won't happen over night though.