One's involved in backing country's diet (7)
I believe the answer is:
regimen
'diet' is the definition.
(a diet is a certain eating regimen)
'one's involved in backing country's' is the wordplay.
'one' becomes 'me' (a setter might use 'one' to humourously mean 'me').
'involved in' is an insertion indicator.
'backing' says the letters should be written in reverse.
'country' becomes 'niger' (African country).
'niger' written backwards gives 'regin'.
'me' put inside 'regin' is 'REGIMEN'.
(Other definitions for regimen that I've seen before include "Merge in for prescribed way of life" , "Method of working" , "Systematic course of treatment, diet, etc" , "Course of diet, therapy" , "(In medicine) a systematic plan for therapy" .)