Indifferent to pressure in new diet (5)
I believe the answer is:
tepid
'indifferent' is the definition.
(I've seen this in another clue)
'pressure in new diet' is the wordplay.
'pressure' becomes 'p' (scientific abbreviation).
'in' means one lot of letters goes inside another.
'new' indicates an anagram.
'diet' is an anagram of 'teid'.
'p' going within 'teid' is 'TEPID'.
'to' acts as a link.
(Other definitions for tepid that I've seen before include "without passion" , "Luke warm" , "Slightly warm" , "Not very warm (water)" , "Of liquid, luke-warm" .)