What does the cryptic crossword clue "Proper idiots in a mess lacking in fibre? (4,8)" mean?

The wordplay uses an anagram. anagram of PROPER + IDIOTS = POORSPIRITED The answer is POORSPIRITED.

Proper idiots in a mess lacking in fibre? (4,8)

Daily Mail Cryptic #17097 | 1 Across | 2023-05-15 flower