Logical food allowance - a pound! (8)
I believe the answer is:
rational
'logical' is the definition.
('rational' is associated in meaning with 'logical')
'food allowance a pound' is the wordplay.
'food allowance' becomes 'ration' (I've seen this before).
'pound' becomes 'l'.
'ration'+'a'+'l'='RATIONAL'
(Other definitions for rational that I've seen before include "Based on logic or reasoning" , "Consistent with reason" , "Capable of thought" , "Endowed with reason" , "Thinking - not a liar (anag)" .)