Strange US diet – belly of fella gets thinner (7)
I believe the answer is:
dilutes
'strange us diet belly of fella gets thinner' is the definition.
I can't tell whether this defines the answer.
'strange us diet belly of fella gets' is the wordplay.
'strange' is an anagram indicator.
'belly of fella' becomes 'l' (I can't justify this - if you can you should believe this answer much more).
'gets' is an insertion indicator.
'us'+'diet'='usdiet'
'usdiet' anagrammed gives 'diutes'.
'diutes' enclosing 'l' is 'DILUTES'.
Can you help me to learn more?
(Other definitions for dilutes that I've seen before include "waters down" , "Thins by adding water" , "Weakens by adding more liquid" .)