If it's interfering with your life to a great extent (or upsetting you a lot and also especially if you have an eating disorder in addition), it is probably a good idea to look into getting a therapist if you haven't already done that.

But, also, have you tried explaining to yourself why your thoughts are "irrational" or "paranoid"? That could possibly help.

Can you distract yourself while you eat? Like read a book or watch a funny TV show or something? That might help if you are really struggling to get calories or something, but Keyslost's suggestion is probably the most effective, sustainable way to address these things.