Problem getting in shape, eat! (7)
I believe the answer is:
consume
'eat' is the definition.
(consuming is a kind of eating)
'problem getting in shape' is the wordplay.
'problem' becomes 'sum' (arithmetic problem).
'getting in' indicates putting letters inside.
'shape' becomes 'cone' (cone is a kind of shape**).
'sum' inserted within 'cone' is 'CONSUME'.
(Other definitions for consume that I've seen before include "Exhaust" , "Devour" , "Use up" , "Eat, drink" .)