One in gym needs meal (3)
I believe the answer is:
pie
'meal' is the definition.
The definition and answer can be both things that one consumes for nourishment as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'one in gym' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in' indicates putting letters inside.
'gym' becomes 'pe' (short for Physical Education).
'i' going into 'pe' is 'PIE'.
'needs' acts as a link.
Can you help me to learn more?
(Other definitions for pie that I've seen before include "what to cook for dinner?" , "Anna's constituent" , "Pastry-covered dish" , "In the sky, this dish is impractical" , "Food baked under pastry" .)