It's blended in a French diet (6)
I believe the answer is:
united
'it's blended' is the definition.
(uniting is a kind of blending)
'a french diet' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'diet' is 'ited' which is present in the answer.
'a french' could be 'un' ('a' in French) and 'un' is located in the answer.
No letters remain.
This explanation may well be incorrect...
'in' is the link.
Can you help me to learn more?
(Other definitions for united that I've seen before include "Agreed" , "Joined together like Manchester soccer team" , "Joined together -- in duet (anag)" , "Of like mind" , "Amalgamated" .)