Extra stout perhaps inside to be sensational (5)
I believe the answer is:
Here is my best explanation:
'extra stout perhaps' is the definition.
I can't tell whether this defines the answer.
'inside to be sensational' is the subsidiary indication.
'inside' says the answer is hidden in the clue.
'obese' is hidden within 'to be sensational'.
(Other definitions for obese that I've seen before include "Too chubby", "Stout", "Very well-upholstered", "Carrying far too much weight", "grossly overweight", "Roly-poly", "carrying remarkable weight", "likely to tip the balance?", "Extremely fat" and "Very big".)