If you dream that you are anorexic, most often this signifies a true-life eating disorder that you have. But if you eat healthfully in your waking life, then this dream signifies your need of spirituality and fulfillment in your waking life. You need more love, friendship or pleasure because you are not getting enough.
If you dream of a friend being anorexic, again this could signify an actual eating disorder they have.
If you’re sure that’s not the case, then it could mean your friend is crying out for more attention and affection.