Hidden danger of wrong sort of fat in tablet (7)
I believe the answer is:
pitfall
'hidden danger' is the definition.
(pitfalls are unexpected dangers)
'wrong sort of fat in tablet' is the wordplay.
'wrong sort of' is an anagram indicator.
'in' means one lot of letters goes inside another.
'tablet' becomes 'pill' (synonyms).
'fat' is an anagram of 'tfa'.
'tfa' placed into 'pill' is 'PITFALL'.
'of' is the link.
(Other definitions for pitfall that I've seen before include "Unsuspected danger or difficulty - for miner?" , "Unexpected problem" , "Hazard" , "Trap in the form of a concealed hole" , "Unexpected difficulty or danger" .)