How is fat free mass calculated?

The calculation of fat free mass is done by subtracting fat mass from total mass. Fat free mass refers to everything in the body except fat tissue, which includes muscle, bone, organs, and water. By taking the total weight of an individual and subtracting the weight of the fat mass, you can accurately arrive at the fat free mass.

This method allows for a clearer understanding of a person's body composition, which is crucial in fields such as obesity medicine, as it provides insight into the proportion of body weight that is not stored as fat. The other options presented do not accurately reflect this relationship; they either incorrectly combine total mass and fat mass or misrepresent the calculations entirely. Thus, the approach of taking total mass and reducing it by fat mass is the correct and standard method used in clinical practice.