What is lean body mass?
Lean body mass contains everything except body fat; that means it counts all the organs, bones, muscles, blood and skin, and everything else which is not fat but has mass.
It is particularly important to know your lean body mass when you are trying to lose weight. By watching your LBM you can control if you are losing only body fat and no muscle. Otherwise, the effect of your diet may be very disappointing, as losing muscle very often results in unpleasant appearance.