Swimmer turned up after exercise for bit of food (6)
I believe the answer is:
peanut
'bit of food' is the definition.
'peanut' can be an answer for 'food' (I've seen this before). I am not sure about the 'bit of' bit.
'swimmer turned up after exercise' is the wordplay.
'swimmer' becomes 'tuna' (tuna is a kind of aquatic vertebrate).
'turned up' shows that the letters should be reversed in order.
'after' says to put letters next to each other.
'exercise' becomes 'pe' (Physical Education).
'tuna' back-to-front is 'anut'.
'anut' put after 'pe' is 'PEANUT'.
'for' is the link.
Can you help me to learn more?
(Other definitions for peanut that I've seen before include "Eat pun for the hard fruit" , "A monkey delicacy" , "Seed also known as a goober" , "Item of fruit" , "Monkey nut" .)