Parliament advice? It's regularly ignored (4)
I believe the answer is:
diet
'parliament' is the definition.
(thesaurus)
'advice? it's regularly ignored' is the wordplay.
'regularly ignored' means one should take alternating letters.
'advice'+'its'='adviceits'
The alternating letters of 'adviceits' are 'DIET'.
(Other definitions for diet that I've seen before include "prescribed nourishment?" , "See 19" , "Attempt to shift a few pounds" , "Food and drink regularly consumed" , "Choice of food" .)