What is the difference between body fat mass and lean mass?

• A. Body fat mass is the amount of fat tissue; lean mass includes muscle, bone, water, and other non-fat tissues.
• B. Body fat mass includes bone and muscle.
• C. Lean mass is fat tissue in muscles.
• D. Body fat mass and lean mass are identical.

Answer: (A)

The main point is understanding what counts as body fat mass versus lean mass in body composition. Body fat mass is the amount of fat tissue in the body. Lean mass includes everything that isn’t fat—muscle, bone, body water, and other non-fat tissues. In other words, lean mass is essentially the fat-free tissues that support movement, structure, and function. So fat mass is stored energy in adipose tissue, while lean mass represents the non-fat tissues that make up the rest of the body's mass. This is why lean mass is not just muscle—bone, organs, and fluids all contribute to it.