Risk of obesity is low apparently (3,6)
I believe the answer is:
fat chance
'obesity is low apparently' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'risk' is the wordplay.
I cannot quite see how this works, but
'risk' could be 'chance' (synonyms) and 'chance' is located in the answer.
The remaining letters 'fat' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'of' is the link.
Can you help me to learn more?
(Other definitions for fat chance that I've seen before include "that won't happen" , "Slender hope (odd though that sounds)" , "Little prospect" , "Slim hope, paradoxically!" , "No likelihood at all!" .)