Allah has provided me with an adequate amount of food, yet I always reject it because of my mental condition of anorexia where I have a fear of gaining weight. Am I sinning?
It is a sin to waste food but it is not s sin to give it to others to utilize it when you don't want to eat it for any reason.
Your mental condition needs proper treatment to be a normal person with out anorexia or any other abnormality.
Wassalam.