Boxer intended to give up a foodstuff (7)
I believe the answer is:
aliment
'foodstuff' is the definition.
(I've seen this in another clue)
'boxer intended to give up a' is the wordplay.
'boxer' becomes 'Ali' (Muhammad Ali).
'intended' becomes 'meant' (to mean something is to intend it).
'to give up' indicates named letters should be taken away.
'meant' with 'a' removed is 'ment'.
'ali'+'ment'='ALIMENT'
(Other definitions for aliment that I've seen before include "Old word for food" , "Something which nourishes - meal tin (anag)" , "Nourishment" , "Sustenance" .)