Those people having little energy for the topic (5)
I believe the answer is:
theme
'the topic' is the definition.
('theme' can be a synonym of 'topic')
'those people having little energy' is the wordplay.
'those people' becomes 'them' (I've seen this before).
'having' means one lot of letters go next to another.
'little' indicates taking the first letters.
The first letter of 'energy' is 'e'.
'them'+'e'='THEME'
'for' is the link.
(Other definitions for theme that I've seen before include "Recurrent unifying idea" , "Musical motif" , "A subject or repeated melody" , "issue" , "Melody on which variations are constructed" .)