Scale weight can be deceiving, especially when it comes to weight loss. A majority of the population does not understand the concept of body composition. Body composition is, to put it simply, what your body is made of.Today body weight can be broken down into two main categories: Lean body mass and body fat mass. Lean body mass is your dry lean mass (muscles, organs, bones, etc) plus your total body water. Body fat mass is your total amount of fat.