Head of State with stomach nearly drained is very thin (7)
I believe the answer is:
scrawny
'very thin' is the definition.
(I've seen this before)
'head of state with stomach nearly drained' is the wordplay.
'head of' suggests taking the first letters.
'with' is a charade indicator (letters next to each other).
'stomach' becomes 'craw' (craw is a kind of stomach**).
'drained' says to hollow out the word (remove centre letters).
'nearly' with its centre taken out is 'ny'.
The first letter of 'state' is 's'.
's'+'craw'+'ny'='SCRAWNY'
'is' acts as a link.
(Other definitions for scrawny that I've seen before include "Skinny" , "Rawboned" , "Skin-and-bones" , "Being underweight" , "Thin and bony" .)