Yes, American's lacking in gluttony (5)
I believe the answer is:
greed
'gluttony' is the definition.
(I've seen this before)
'yes american's lacking' is the wordplay.
'yes' becomes 'agreed' (I've seen this before).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'lacking' is a deletion indicator.
'agreed' with 'a' taken away is 'GREED'.
'in' is the link.
(Other definitions for greed that I've seen before include "Selfish desire" , "Insatiability" , "Rapacious desire" , "selfish habit" , "Immoderate desire" .)