The amount eaten will produce serious complaint (11)
I believe the answer is:
consumption
'complaint' is the definition.
(consumption is a kind of disease)
'the amount eaten will produce serious' is the wordplay.
I cannot quite see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'amount' could be 'pi' (pi is a kind of amount) and 'pi' is found in the remaining letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for consumption that I've seen before include "Eating" , "Wasting disease" , "See 7" , "that may be conspicuous" , "disorder" .)