4-Compartment Model (Criterion)
The Reference Standard in Human Body Composition Research
The four-compartment (4C) criterion model is the undisputed scientific benchmark in clinical body composition assessment. While two-compartment (2C) methods assume fixed constants for tissue density and hydration (such as assuming fat-free mass is always exactly 73.2% water), the 4C model directly measures every variable, eliminating biological estimation error across diverse ages, ethnicities, and clinical conditions.
The Four Measured Components
By integrating three independent physical modalities alongside calibrated body weight, the 4C model partitions total body mass ($M$) into four distinct chemical compartments:
\[M = \text{Fat Mass} + \text{Total Body Water} + \text{Bone Mineral} + \text{Residual (Protein/Glycogen)}\]- Body Volume ($BV$): Measured via Air Displacement Plethysmography in the Bod Pod.
- Total Body Water ($TBW$): Measured via Deuterium Dilution ($^2\text{H}_2\text{O}$) stable isotope spectroscopy.
- Bone Mineral Content ($Mo$): Measured via whole-body Dual-Energy X-Ray Absorptiometry (DXA).
- Total Body Weight ($BW$): Measured on a calibrated clinical scale.
Criterion Mathematical Formulation
Fat mass is calculated using the validated Fuller and Wang 4-compartment equation:
\[\text{Fat Mass (kg)} = 2.747 \times BV - 0.710 \times TBW + 1.460 \times Mo - 2.050 \times BW\]Residual cellular dry mass (primarily metabolically active skeletal muscle protein and viscera) is then resolved:
\[\text{Residual Protein (kg)} = BW - (\text{Fat Mass} + TBW + Mo)\]Why Choose the Criterion 4C Model?
- Zero Hydration Assumption: Accurately assesses athletes, fluid-retentive patients, sarcopenic individuals, and pediatric populations where standard 2C assumptions fail.
- True Density Resolution: Distinguishes between changes in muscle protein, intracellular hydration, and bone density during longitudinal interventions.
- Reference Validation: Serves as the primary validation anchor against which new imaging, optical scanners, and AI algorithms are calibrated.
What You Take Home
- Comprehensive 4-compartment analytical report detailing absolute (kg) and percentage (%) values for Fat, Water, Mineral, and Protein.
- Measured hydration of fat-free mass ($TBW / FFM$), providing direct clinical insight into intracellular vs. extracellular fluid status.
- Comparison of criterion findings against 2-compartment DXA and Bod Pod standalone reports.