Showing you've put on weight, having been drinking too much (5)
I believe the answer is:
tight
'much' is the definition.
Both the definition and answer are adjectives. Perhaps there's an association between them I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for tight that I've seen before include "Closely constrained, constricted" , "Squeezed" , "Parsimonious" , "with limited room to manoeuvre" , "Unlikely to be choosing the present" .)