Healthy intake had parliament on a knife-edge? (8,4)

'healthy intake' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'had parliament on a knife-edge?' is the wordplay.
'had' becomes 'd' (in contractions e.g. 'I'd', 'you'd' etc).
'parliament' becomes 'diet' (I've seen this before).
'on' is a charade indicator (letters next to each other).
'a knife-edge?' becomes 'balance' (I am not sure about this - if you are sure you should believe this answer much more).
'd'+'diet'='ddiet'
'ddiet' put after 'balance' is 'BALANCED DIET'.

Can you help me to learn more?