Lecture on Body Composition

Overview

• Body Composition: Analysis of body makeup regarding different tissues.
• Will cover techniques to measure or estimate body composition.

Definitions

• Fat Mass (FM): Inactive tissue.
• Fat-Free Mass (FFM): Also known as lean tissue, burns energy (e.g. muscle, organs).

Models of Body Composition

1. Chemical Model: Analyzes fat, protein, carbs, water, minerals.
2. Anatomical Model: Considers adipose tissue, muscle, organs, bone, and others.
3. Two-Component Model: Most common approach.
   • Fat Mass: Inactive tissue.
   • Fat-Free Mass: Active tissues like muscle, bones, organs.
4. Binky Two-Component Model: Breaks fat mass into essential and non-essential fat.

Significance of Body Composition

• Indicator of Nutritional and Health Status: Helps in assessing energy balance.
  • Energy Balance: Energy in vs. energy out.
  • Identifies conditions like obesity, anorexia, sarcopenia, osteoporosis.
• Separate Metabolically Active Tissues: FFM used to normalize physiological measures, e.g., VO2 to lean mass.
• Determine Desirable Weight: Uses body fat percentage and body weight to set goals.

Measuring Techniques

1. Direct Methods: Anatomical dissection or chemical analysis (not feasible).
2. Indirect Methods: Measure variables to predict body composition.
   • Hydrostatic Weighing: Measures body density via underwater weighing.
   • Air Displacement Plethysmography (Bod Pod): Uses air displacement.
   • DEXA: Dual-energy X-ray absorptiometry, gold standard.
   • MRI: Magnetic resonance imaging.
   • Field Techniques: Skinfold caliper, Bioelectrical Impedance Analysis (BIA).

Densitometry

• Body Density (DB): Mixture of FM and FFM densities.
• Hydrostatic Weighing: Uses Archimedes' Principle, measures weight underwater.
  • Calculate body volume from displaced water.
  • Siri Equation: Estimates body fat percentage.
• Air Displacement Plethysmography (Bod Pod): Measures air displacement.
  • Accurate but can have errors due to excess body hair, movement, and claustrophobia.
• DEXA: Provides three-component model (FM, FFM, bone density).
  • Highly accurate and detailed regional composition.

Field Techniques

• Skinfold Method: Estimates body fat using subcutaneous fat thickness.
  • Different sites measured (e.g., chest, abdomen, thigh).
  • Requires practice to be accurate.
  • Procedures for ensuring consistency.
• Bioelectrical Impedance Analysis (BIA)*: Uses electrical signals to measure body composition.
  • Conductivity affected by hydration levels.

Body Mass Index (BMI)

• BMI: Weight (kg)/height (m)^2.
  • Categories: Underweight, Normal, Overweight, and Obesity (Class 1, 2, 3).
  • No Direct Body Composition Measure: Only a predictor of mortality.

Waist-to-Hip Ratio

• Indicator for Cardiovascular Disease: Measures central adiposity.
  • Normal ranges:
    • Males: Close to 0.8
    • Females: Close to 0.7

Desired Body Weight Calculation

• Uses current body weight and body fat percentage to calculate target weight for a desired fat percentage.

  • Formula:

    Desired Body Weight = Current Body Weight - (Current % Fat x Current Body Weight) / (1 - Desired % Fat) 
    

Conclusion and Assignment

• Metabolic Syndrome: Research criteria and potential treatments.
• Questions: Post to Canvas discussion tab for responses.