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' says to take the initial letters.
'between' indicates putting letters inside.
'gym' becomes 'pe' (short for Physical Education).
'and' is a charade indicator (letters next to each other).
'work' becomes 'toil' (toil is a kind of work).
The first letters of 'appear newly ubiquitous' is 'anu'.
'pe'+'toil'='petoil'
'anu' going inside 'petoil' is 'PEANUT OIL'.