Just catching up PureH20 as not been around.
There is of course some muscle wastage on a fast to provide glycogen from amino-acids, but this is reduced to a minimum during protein-sparing, otherwise our vital organs would be used for feeding from the outset.
Liver and kidney stress or even heart-muscle attrition only occur when entering pathological starvation, and before this occurs, the body always signals the return of natural and very intensive hunger. I have even known fasters to almost reach the skeletal condition with no ill-effects, but only benefit and of course were supervised by experienced personnel.
The fastest way to lose excess weight is to adhere to a low calorie but nutrient dense way of eating, or what is known as being Nutritarian (50 pounds in 30 days or so) as this maintains a normal metabolic rate, whereas this is significantly lowered while water-only-fasting to conserve food reserves.