Whole body composition Flashcards
What are the strengths and limitations of body composition analysis?
- Can track epidemiological differences and changes
- Determine the true efficacy of interventions
- Assesses health risk
- Determines the cause of weight change (sarcopenia)
- Limitations - All in vivo methods for whole-body composition are estimations
- relative body fat % error of 3-4%
What is the difference in water and fat composition in the human body?
- Males : water = 62%, Fat = 14%
- Female : water = 52%, Fat= 25%
- Muscle has ~75% water , Fat - 10%
What are the sex differences in body composition?
- Four times greater essential fat for femalws relates to child bearing
- Avg young male possesses begween 12-15% body fat
- Avg young female possesses between 25-28% of body fat
What are the % body fat classifications in males?
low = less than 5%,
normal = 6-24%
too high >25%
What are the % body fat classifications in females?
Low = less than 8%
Normal = 9-31%
High = greater than 32%
What are age-associated differences in body composition?
- Density of FFM is lower in children than adults
- Female density of FFM is lower at each age than males
- Percentage of FFM that is composed of water is higher in children (Fat free mass)
What are some in vitro methods ( direct assesment) for body composition analysis?
- Anatomical dissection of cadabers
- Chemical analysis = dissolves body into fat and fat free components
What are some in vivo methods for body composition analysis?
- Whole body:
- hydrostatic weighing
- Air displacement
- Electrical properties e.g. bio-electrical impedance (BIA/0
- Dual-energy X-ray absorptiometry (DXA/DEXA)
Regional :
- subcutaneous adipose tissue
- Ultrasounf
- Near infra-red tolerance
- CSA:
- Skinfolds + Circumferences
- Computed Tomography
- Magnetic resonance imaging
Estimations : Anthropometry to estimate body composition
What is magnetic resonance imaging?
- Electromagnetic radiation, not ionising radiation, in strong magnetic field excites hydrogen nuclei of body’s water and lipid molecules. Nuclei then project detectable signal to visually represent various body tissues
- Provides quantitative info on total and subcutaneous adipose tissue
What is hydrostatic weighing
- Based on archimedes principle of water displacement
- Loss of weight in water = weight of water displaced which yields volume of water displaced at any temp
- Weight in air - weight underwater = weight of water = displaced
What are some advantages and disadvantages of hydrostatic weighing?
- used to be considered gold standard
- Scientifcally sound principle for body volume
- no radiation exposure
-Disadvantages - Assumes density of fat and lean are constant (not true as differences in bone and muscle density)
- Assumes GI gas volume is constant
Limitations: - measurement of residual lung volume
- Precision of underwater weight
- Cost
- Non-portable
- Not suitable for all subjects
What is air displacement plethysymography (BODPOD)?
- Measures body volume by air displacement
- actually measures pressure changes with injection of known volume of air into closed chamber
- Large body volume displaces air volume in chamber
- results in bigger increase in air pressure with injection of known volume of air
- High validity compared to hydrodensitometry
What is bioelectrical impedance analysis (BIA)?
- measures imedpance (opposition) by body tissues to the flow of a small (less than 1mA), alternating electrical current (50 kHz)
- Impedance is a function of:
- Electrical resistance of tissue
- Electrical capacitance (storage) of tissue (Reactance)
- Hydrated, fat-free body tissues and extracellular water facilitate electrical flow compared to fat tissue because of greater electrolyte content of fat-free component
What is BIA theory?
- The body can be considered to be a series of cylinders
- Resistance is proportional to the length of the cylinder
- Resistance is inversely proportional to the CSA
- Volume = the length of the cylinder times its area
- Knowing the resistance and the length, one can calculate volume
- Assuming that the current flows past through the past of least resistance (water), then the volume determined is that of body water
What are the types of BIA ?
- Impedance
- Sensing electrodes, current electrodes
- Scale + BIA analyser - metal plate electrodes
What are the advantages and disadvantages of BIA?
- Relatively inexpensive
- portable
- Quick and non-invasive
Assumptions:
- the body is a series of cyclindrical units
- assumes the homogenous body composition
- Assumes a large limb contribution
Limitations:
- Low accuracy & precision
- No worse than hydrodensitometry
- Variation between manufactures/models
- Very sensitive to hydration, temp and electrode position
What is near infra-red interactance?
- Records optical densities which are linearly related to subcutaneous (and total) body fat when entered into predictive equations
- Uses tech developed by US dept Agriculture to assess body comp of livestock and lipid content of grains
- Normally used as a single site measure at the biceps
- Does not accurately predict human body fat across broad range of body fat levels
What is anthropometry?
includes measure of :
- skinfolds
- height
- weight
- width
- circumferences
What are skinfolds?
- common field method
- Measures double thickness of skin and subcutaneous fat
- Relationships among selected skinfold sites and body density
- Caliper experts constant tensuon of 10g/mm2
- Sum of skinfold indicates relative fatness of individual
What are advantages and disadvantages of skin fold measurements?
- Inexpensive
- Quick
- Portable
- Large ref database
- Assumptions :
- predicts non-subcutaneous fat
- Sites represent avg thickness of all sub fat
- Compressibility of fat similar between subjects
- Thickness of skin negligible
Limitations:
- technician error
- skinfold thickness affected by factors other than amount of fat ( hydration, oedema, dermatitis)
- Poorly predicts visceral fat
What are single site measurements?
- Tricep skinfold thickness
- Subscapular skinfold thickness
- Not for estimating body fat determination
- for comparing against other reference data
Two site measurements:
- Tricep SF and Subscapular SF is correlated with body fatness in children
- Tricep SF and calf SF is correlated in adults
Multiple site measurements :
- Many sites
- Many equations
What are circumferences?
- Uses 3 sites
- men : right forearm, abdomen, right upper arm or buttocks (27+)
- Women: abdomen, right thigh, right forearm or right calf(27+)
- Easy to do
- Gives pattern of fat distribution
- Can be used for predicting body fat %
- LIMITATION: Very limited database
What is computed (Axial) tomography?
- Generates detailed cross-sectional, 2 dimensional radiographic images from many x-rays taken at diff angles
- Passes x-ray beam through tissues of different densities
- Provides quantitative information on:
- Total tissue area
- Total fat and muscle area
- Thickness and volume of tissues within an organ
- LIMITATION : High radiation exposure
