You don't need a nutritionist to tell you to stop eating junk/processed food. All other diet advice are pure b.s. as there's no scientific answer to what "a proper diet" is. What is "healthy" and what is not changes on a similar rate as weather broadcast i.e. see a recent turn on fat.

Which vitamin or mineral deficiency leads to psychosis? (With a link to this scientific proof please)

Both can cause mental symptoms (retardation for example). But both are rare.