Dieting furiously getting fired up (7)
I believe the answer is:
ignited
'fired up' is the definition.
(I've seen this before)
'dieting furiously' is the wordplay.
'furiously' is an anagram indicator.
'dieting' is an anagram of 'IGNITED'.
'getting' acts as a link.
(Other definitions for ignited that I've seen before include "Set on fire" , "Sparked off" , "Gin diet (anag.)" , "fired" , "Caught fire" .)