Lean Body Mass is everything but the fat on your body… muscles, bones, organs, etc. It is only an estimate. It is rally hard to dissect the body of fat and put it back on and get an accurate measurement.
Healthy ranges for men are between 15% – 20%. At 15% you have flat abs, at 20% you have the start of a ponch, and at 10% you have six-pack abs.
Healthy ranges for women are between 20% – 25%. At 20% you have flat abs, at 25% you have the start of a ponch, and at 15% you have six-pack abs.
Remember too lean and too fat are both unhealthy!