He eats a lot - too much, putting weight on (7)
I believe the answer is:
glutton
'he eats a lot too much' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'putting weight on' is the wordplay.
'putting' becomes 'glut' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'weight' becomes 'ton' (unit of weight).
'on' is a charade indicator (letters next to each other).
'glut'+'ton'='GLUTTON'
Can you help me to learn more?
(Other definitions for glutton that I've seen before include "Immoderate eater" , "One eats too much" , "Over-eater" , "Pig" , "Forest animal" .)