There are numerous ways you can do this...I have went down as low as 10 X's my bodyweight and never lost too much muscle. However, another way you can go about this is to start at a low calorie level (like 10 X' BW) and add calories every week or so. The later is something MS has stated doing in the past, and I would be a fool to overlook this method (never tried it) in both seeing her past pictures and her credentials.
The first method all you do is start at a level 0f 14-15 times your bodyweight for the beginning. When this no longer is effective, then you can drop down to 13-14 calories times your bodyweight. I have done this to levels of 8-10 times my bodyweight and had no real problems as long as I didn't overdue my activities, etc... However, I almost never go below 10 unless I am getting ready for an event like the Olympia or something...oh sorry, I mean the beach or special events in the year...lol.
The second method is kind of the opposite of the first one...it helps keep the body "upregulated" (I really need to think of a better term than that) before it reaches points of working against you. Since I have never tried this method, maybe if MS reads this post, she can elaborate on it a little better. It just makes sense when you think about it.
Maybe this gives ya some food for thought...
BMJ