What is "lean mass" and "fat mass"?
Lean mass is your total body weight minus fat; it's that simple. Your fat mass is your total pounds of fat on your body. For example, if you weigh 100 pounds, and you have a fat mass of 30, that means you have 30 pounds of fat on your body. Again, just the opposite is so for the lean mass. So, if you weigh 120 pounds, and your lean mass is 100, that means 100 pounds of your weight is everything but the fat.