I have never heard being authentic equated with what "feels good." So I guess I don't agree with what you've written. For me, being authentic is expressing one's true self, not hiding, not pretending to be something one's not, having one's inner and outer selfs come into congruence. For me, it doesn't have much to do with seeking out what feels good, like eating junk food as in your example. It may indeed feel good to be authentic but that doesn't mean that all things that feel good (eating favorite foods) are part of being authentic.