for me, my BMR almost always is the same using various calculations, it is when I start working in the activity level that messes me up. So I just try to make sure I stay below BMR but not too far below and figure it will work itself out.
I am totally with Pebbles regarding the eat when you are hungry situation. If I was any good at that I would not be here trying to lose weight. I also think that long before your body starts to eat its own muscle, you get into serious cravings and binge eating.
Anyone ever read this study?....They Starved So That Others Be Better Fed: Remembering Ancel Keys and the Minnesota Experiment I read the book and I will tell you that it is amazing what the human body will do to try to get the nutrition it needs.