Lecture 2: Measuring Body Composition 1 Flashcards
What is the two-component model?
Fat mass (FM) + fat-free mass (FFM)
What does the two-component model assume?
Assumes the total body mass is composed of two components and the densities of each component are known and the same for all individuals (E.g. FFM is constant)
What is the three-component model?
Fat mass (FM) + (Bone mineral content + Bone-free fat-free mass)
What is bone-free fat-free mass?
Lean tissue mass
Why do we measure body composition?
- Health
- Sports performance
- Monitoring growth
- Assessing response to intervention
- Creation of reference values
- Population monitoring
High body fat in the ?? area is associated with increased health risks
Abdominal
How do we measure fat % of total body composition?
%fat = (FM / body weight) x 100
How do we measure free fat mass (FFM) % of total body composition?
%FFM = (FFM / body weight) x 100
What is regional body composition?
Whether fat is stored primarily in the central or peripheral regions
Health risks of obesity depend on ??? as well as total body composition
Regional fat distribution
What is a android fat distribution?
Central = Fat accumulation in the abdominal area, leading to an “apple-shaped” body
What is gynoid fat distribution?
Peripheral = fat is stored in the hips, thighs, and buttocks leading to a “pear-shaped” body
What type of fat is android distribution? (Central)
Visceral fat - stored deep within the abdominal cavity around vital organs like the liver, pancreas, and intestines.
What type of fat is gynoid distribution? (Peripheral)
primarily subcutaneous fat (stored under the skin)
Why is central worse than peripheral?
- metabolically active
- contributes to chronic inflammation
- increases risk of heart disease and diabetes
- impacts organ function.
What shape do women tend to be?
More gynoid (peripheral)
What health risks does central adiposity increase?
- T2D
- CHD
- CVD
- Arthritis
- Hypertension
What is central fat composed of? (Equation)
Central fat = visceral (intra-abdominal) and subcutaneous (under the skin) fat
What are some ways to measure total body composition? (2 component model)
- Underwater weighing
- Air displacement plethysmography
- BIA
- Anthropometry
What are some ways to measure regional body composition?
- CT
- MRI
- DXA
What are the three main types of approach for the two-component model?
- Densitometry
- Electrical resistance of the body
- External measurement
What are examples of measuring densitometry?
- Underwater weighing
- Air displacement plethysmography
What is an example of measuring electrical resistance of the body?
Bioelectrical impedance analysis (BIA)
What is an example of taking an external measurement?
Anthropometry
What is the equation for density?
mass/volume
What is the main densitometry equation used to calculate %fat from total body density?
Siri:
%Fat = ((4.950/D) - 4.500) x 100%
What are assumptions that are made when using densitometry?
- Density of FFM is constant
- Density of Fat does not vary
- Water content of FFM is constant
- Proportion of bone to FFM is constant
What is underwater weighing?
measuring a person’s body density based on their weight underwater compared to their weight on land
What are the advantages to underwater weighing?
- “gold standard”
- Accurate
- 2% error
What are the limitations to underwater weighing?
- density of FFM not necessarily uniform
- do 4-12 times
- not suitable for all
- breathing apparatus to measure lung volume
- bulky equipment
What is air displacement plethysmography?
Similar principle to underwater weighing except calculate displaced air rather than displaced water
What is bioelectrical impedance analysis (BIA)?
Body conducts electricity through FFM - pass weak current through body and measure impedance to current
What is impedance?
Converts (resistance + reactance) to estimate FFM
How is BIA calculated?
- FFM predicted from TBW estimates
- FM then derived as difference between body weight and FFM
What percent of FFM is water?
approx. 73%
What can the validity of BIA be impacted by?
- hydration status
- recent PA
- food consumption
- menstrual status
- body position
What is good practice for BIA?
- avoid alcohol & vigorous exercise 24-48 hours before
- measure >2h after eating and within 30 min of voiding
- lie down with limbs not touching body
How do you improve the measurement of BIA?
By adding sex and age
What are the advantages of BIA?
- simple
- cheap
- portable
- suitable for all ages
What are the limitations of BIA?
- need to be fasting
- control recent activity & hydration status
- need appropriate equation
What is the most widely used method of measurement?
Anthropometry
What does anthropometry involve?
BMI, skinfolds, circumferences, breadths
How do we interpret anthropometry measurements?
- compare results with reference data
- using cut offs that relate to risk
What does anthropometric reference data need to be?
- developed from group representative of healthy population
- need to be specific (age, gender, ethnicity)
What are percentiles?
Describe the position of the measurements in relation to the measurements for a population
What are the advantages to anthropometry?
- simple
- safe
- noninvasive
- cheap
- portable equipment
- commonly used for large studies
What are the limitations to anthropometry?
- less accurate so less sensitive to change
What are potential sources of error for anthropometry?
- measurement error
- variation in tissue composition
- assumptions may not be valid in disease states or obesity
