Biscuit treatise showing food's journey (9,5)

I believe the answer is:

digestive tract

I'm a little stuck... Click here to teach me more about this clue!

'food's journey' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

'biscuit treatise' is the wordplay.
'biscuit' becomes 'digestive' (type of biscuit).
'treatise' becomes 'tract' (tract is a kind of treatise).
'digestive'+'tract'='DIGESTIVE TRACT'

'showing' acts as a link.

Can you help me to learn more?

(Another definition for digestive tract that I've seen is " Alimentary canal".)

I've seen this clue in The Daily Express.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.