Fat starts to appear newly ubiquitous between gym and work (6,3)

'fat' is the definition.
(peanut oil is a kind of fat)

'starts to appear newly ubiquitous between gym and work' is the wordplay.
'starts to' suggests taking the first letters.
'between' means one lot of letters goes inside another.
'gym' becomes 'pe' (Physical Education).
'and' means one lot of letters go next to another.
'work' becomes 'toil' (toil is a kind of work).
The initial letters of 'appear newly ubiquitous' is 'anu'.
'pe'+'toil'='petoil'
'anu' going inside 'petoil' is 'PEANUT OIL'.