Mentioned a noted new diet (5)
I believe the answer is:
cited
'mentioned' is the definition.
('cite' can be a synonym of 'mention')
'a noted new diet' is the wordplay.
I cannot really see how this works, but
an anagram of 'diet' is 'ited' which is present in the answer.
A single letter 'c' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for cited that I've seen before include "Called for" , "Made reference to -- edict (anag)" , "Quoted or mentioned as example" , "Summoned" , "Commended" .)