What are the two main components of body composition?

The two main components of body composition are fat mass and lean mass. Fat mass includes all the fat tissue in the body, which can be subcutaneous (under the skin) or visceral (around internal organs). Lean mass encompasses everything else—this includes muscle, bones, water, organs, and connective tissues. Understanding the distinction between these two components is crucial for assessing health and fitness levels. For example, a person may weigh the same as someone else but have a very different proportion of fat mass to lean mass, impacting health risks and performance.

While body mass and muscle mass touch on relevant ideas, they do not encompass the full spectrum of body composition since muscle is only a part of the lean mass category. Similarly, body weight and water weight are too simplistic and do not account for fat mass. Density mass and bone mass also do not accurately represent the complete picture of body composition, as bone mass is just one element within the broader framework of lean mass.