Are Lean Body Mass and Fat-Free Mass the Same or Different Body Components? A Critical Perspective

Area of Science:

• Body composition research
• Physiology
• Nutritional science

Background:

• The 2-component model of body mass (fat and fat-free mass) is fundamental in body composition studies.
• The terms lean body mass (LBM) and fat-free mass (FFM) are often used interchangeably, causing confusion in scientific literature.

Purpose of the Study:

• To clarify the chemical distinctions between LBM and FFM.
• To resolve the longstanding ambiguity regarding the equivalence of LBM and FFM in body composition science.

Main Methods:

• Retrospective analysis of classical and refined body composition models.
• Review of lipid organization and extraction methodologies.
• In-depth analysis of historical and contemporary scientific discourse on body composition terms.

Main Results:

• Fat-free mass (FFM) is experimentally derived and includes polar or structural lipids, equivalent to Behnke's "essential" fat.
• Lean body mass (LBM), as originally conceptualized, shares the same chemical composition as FFM.
• The term FFM is chemically accurate and encompasses essential lipids, while LBM is largely historical.

Conclusions:

• Lean body mass (LBM) and fat-free mass (FFM) are chemically the same.
• The scientific community should adopt FFM as the precise term, eliminating the duplicative and potentially confusing LBM.
• Using FFM exclusively will enhance clarity in body composition research and related fields.