Just to point out, people who have a higher weight, and body fat percentage who make drastic changes in their eating habits as in cold turkeying unhealthy habits can lose a lot of weight, very, very quickly without the loss of muscle mass, simply put the body was ready for it.
For me for example on my nutrition ideas, I lost 10, then 8, then 6 in the first 3 weeks of my attempt to begin eating entirely healthy and giving up soda and energy drinks. That's 24 pounds in 3 weeks. I was eating roughly 1600 calories a day at the time with minimal to no exercise.
My guess is that the reason such unnaturally high numbers can show up on the scale and not be having a loss of muscle mass is that there might be more to our bodies then we quite yet understand.
Because quite frankly, it is impossible to lose that much weight in a unhealthy manner when you at the same time feel great while doing it, especially six weeks in. If there were muscle mass being lost, for that long, a person wouldn't feel all that great.
I believe that in some cases, with some metabolisms and body sizes, massive numbers can in fact be possible while not losing muscle mass.
That also said, I believe that science or no, as your body shrinks, we are physically incapable of retaining as much water as we were able to before. Thus as we shrink down, the amount of stored water our bodies can keep within it also decreases. There probably isn't an exact science to it, but I'd be willing to bet if you took 30 pounds away from someone, they would be less capable of storing a number of pounds of water in their bodies anymore.
I just felt like contributing is all