Student's less fat eating recipe (7)
I believe the answer is:
learner
'student's' is the definition.
(thesaurus)
'less fat eating recipe' is the wordplay.
'less fat' becomes 'leaner' ('lean' can be the opposite of 'fat' so perhaps 'leaner' is reasonable for 'less fat').
'eating' means one lot of letters goes inside another.
'recipe' becomes 'r' (abbreviation).
'leaner' placed around 'r' is 'LEARNER'.
(Other definitions for learner that I've seen before include "A student or beginner" , "One being taught" , "He displays the L-plate" , "Pupil or apprentice" , "Amateur" .)