Fine results in going beyond this potentially simple diet (5,5)
I believe the answer is:
speed limit
'fine results in going beyond this' is the definition.
The definition suggests a singular noun which matches the answer.
'potentially simple diet' is the wordplay.
'potentially' is an anagram indicator (letters have the potential to spell a new word).
'simple'+'diet'='simplediet'
'simplediet' is an anagram of 'SPEED-LIMIT'.
Can you help me to learn more?
(Other definitions for speed limit that I've seen before include "maximum rate by law" , "Any faster might generate a fine" , "Fine results maybe after exceeding this" , "seventy, at most" , "maximum going rate?" .)