Row about upper-class B&B offering more fat (7)
I believe the answer is:
tubbier
'more fat' is the definition.
('tubby' can be similar in meaning to 'fat')
'row about upper-class bb' is the wordplay.
'row' becomes 'tier' (tier is a kind of row**).
'about' means one lot of letters goes inside another.
'upper-class' becomes 'u' ('u' can be similar in meaning to 'upper-class').
'u'+'bb'='ubb'
'tier' enclosing 'ubb' is 'TUBBIER'.
'offering' acts as a link.
(Other definitions for tubbier that I've seen before include "Squatter" , "Comparatively flabby" , "round a bit more" .)