Having no food, isn’t worried; gets a cigarette out (7)
I believe the answer is:
fasting
'having no food' is the definition.
I can't tell whether this definition defines the answer.
'isn't worried gets a cigarette out' is the wordplay.
'worried' is an anagram indicator (worry can mean to interfere with or disturb).
'gets a cigarette' becomes 'fag' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'out' is an insertion indicator.
'isnt' is an anagram of 'stin'.
'stin' going within 'fag' is 'FASTING'.
Can you help me to learn more?
(Other definitions for fasting that I've seen before include "not eating" , "Going without food" .)