Body Composition Overview
Body Composition Overview
Body composition refers to a descriptive breakdown of the body's makeup.
It can be analyzed through different models, primarily distinguishing between fat mass (FM) and fat-free mass (FFM).
2-Component Model
The 2-component model includes:
Fat Mass (FM)
Fat-Free Mass (FFM)
Breakdowns for Adults
Men:
Water: 55-65%
Fat: 15-20%
Protein: 16-18%
Mineral: 5.8-6.0%
Women:
Water: 55-65%
Fat: 20-30%
Protein: 14-16%
Mineral: 5.5-6.0%
Expanded Models
3-component model includes FM, lean mass (LM), and bone.
4-component model includes FM, LM, bone, and water.
Body Composition Models
2-Component Models (2C)
The 2-component models are based on the density of fat mass and fat-free mass.
Characteristics include:
Cost-effective
Fast implementation
Commonly used in field testing
Initial methods developed in this domain
Common examples include:
Skinfold measurement
Bioelectrical Impedance Analysis (BIA)
Noted for:
Poor precision with a typical accuracy within ±5%.
Body Composition by Population Metrics
Body composition metrics can vary significantly based on factors such as:
Age
Gender
Race or ethnicity
Example metrics include:
African-American (Female):
Body Density (Db): Approx. 1.088
% Body Fat equation:
Asian (Japanese Male):
Body Density (Db): Approx. 1.099
% Body Fat equation:
Clinical populations and variations with specific examples:
Anorexia Nervosa (Female, Age 15-44):
Body Density (Db): with density reference of 1.101
Several diverse age groups display varied body fat percentages.
Hydrostatic Weighing
Sources of Error:
Variation exists between individuals regarding the distribution of FFM made up of water, mineral, and protein.
Bone density variations and total body water fluctuations.
Less validity in children, women, the elderly, and athletes.
Issues with measuring residual lung volume - the volume of air left in the lungs after maximum exhalation.
Subjectivity in fear of being underwater.
Accuracy: ± 1.5% - 4% with a precision of Coefficient of Variation (CV%) ranging from 2-5%.
Air Displacement Plethysmography
Sources of Error:
Similar issues as hydrostatic weighing regarding variations in FFM assumptions.
Influences from bone density variations, residual lung volume, excessive clothing, and body hair trapping air.
Accuracy: ± 3% with precision CV% of 3-5%.
Body Composition Models (2C) Continued
Various electrical impedance methods depend significantly on total body water (TBW) measurements.
Accuracy: 2-4% with a CV% of 3-7%.
Bioelectrical Impedance
This method measures the impedance to electric current flow, which reflects tissue properties:
High-water-content tissues (such as muscle) are conductive.
Fat, bone, and air-filled spaces exhibit poor conductivity.
FFM in relation to body height and impedance is inversely related: .
New InBody TBW Considerations
Hydration status is crucial for accurate BIA assessments and significantly impacts the precision of InBody results.
New technology allows for assessing TBW within a standard range, enhancing confidence in longitudinal assessments as long as hydration levels are monitored consistently.
Skinfold Thickness Measurements
Accuracy: 2-4% with a CV% of 3-7%.
Dependent on skill level of the tester.
Performance can deteriorate with increased body fat.
Practical for field use due to low cost and ease of implementation.
Body Composition Models (3C) and (4C)
The 3-component model consists of FM, lean mass (LM), and bone, commonly exemplified by Dual-Energy X-Ray Absorptiometry (DXA).
Accuracy: ± 2% and a precision CV% of <2%.
The 4-component model incorporates FM, Lean Mass (LM), Bone, and Water:
Requires multiple tests (e.g., DXA and TBW).
Time-consuming but yields the most accurate results within ± 3% of real values.