What is the difference between fat-free mass and lean mass?
Overview
Section titled “Overview”The terms “fat-free mass” and “lean mass” are often used interchangeably, but they have different meanings in body composition assessment. Confusing them can lead to misinterpretation of results.
Details
Section titled “Details”- Fat-free mass (FFM) is everything in the body that is not fat — this includes muscle, bone, water, organs, and connective tissue
- Lean mass (or muscle mass) refers specifically to skeletal muscle tissue
- Devices using a 2-compartment model (such as BIA, Bod Pod, and Hydrostatic Weighing) report fat-free mass, not lean mass
- A result labeled “fat-free mass” on a 2-compartment report should not be interpreted as a direct measure of muscle
- If knowing true lean/muscle mass is important for a client’s goals or clinical needs, consider a device or model that separates out additional compartments (e.g., a DEXA-based 3-compartment model)
- Styku’s 3D body scanning can complement compartment-model devices by tracking shape and circumference changes over time
Applies to: All Styku configurations; general body composition assessment context
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