As a Marine who has gone through many, many building and leaning cycles, I call BS on this. When you drop that fat, you aren't actually losing muscular tissue (at least not much). I've gotten down to Olympian levels of body fat, 9-10%, and what you are losing besides the fat is water weight. Your muscles shrink because they hold in less blood; your body regulates this to keep blood pressure normalized with all the decrease in fatty tissues. At less that 8% (on average, for men at least), most bodies will start to break down and metabolize muscle tissues (started happening to me around 9%, and was NOT a fun experience).