Body Composition Status & Assessment
What are issues associated with the Bod Pod?
- Air trapped within clothing and body hair (facial and body hair will underestimate fat mass) - Variations in temperature and air movement in room - Claustrophobia - Body temperature - Equation used (Siri vs. Brozek)
What principles are BIA based on ?
- Lean tissue (mostly water and electrolytes) is a good electrical conductor (low impedance) - Fat tissue is a poor electrical conductor (high impedance)
Issues with hydrodensitometry
- Residual volume must be measured or estimated - Gas can be trapped in the GI tract - Participant must be able to exhale all air underwater and remain still for several seconds - Density of FFM is assumed constant between individuals
What principles are skinfold measurements based on ?
- Subcutaneous fat is proportional to the total amount of body fat - 1/3 of total fat is located subcutaneously
What are issues associated with skinfold measurements?
- The amount of technician training and technique - the accuracy - the appropriate use of calibrated calipers - the equation used - increased difficulty in obese clients
What are issues associated with DEXA?
- Very expensive - Radiation exposure
What issues are associated with BIA?
- client following instructions: hydration status, exercise... etc. affect BIA - prediction equation used increases error - activity level reported - assumes body is shaped like a cylinder with a uniform length and cross-sectional area (body segments are not uniform)
What are issues associated with CT/MRI scans?
- not very practical due to cost and/or radiation exposure (CT scans)
Excess body fat is related to:
- type 2 diabetes - hypertension - dyslipidemia - cardiovascular disease - certain types of cancer (breast cancer, colorectal) - premature death/increased number of YPLL (years of potential life lost)
air displacement plethysmography
-Body composition assessment technique based on same principle as hydrostatic weighing -Uses air instead of water.
Ultrasound assessment
-measures fat thickness same sites as skinfold measurements - not sensitive to caffeine and hydration status like BIA
What compartment model is BIA?
2C model: FM & FFM
What compartment model is hydrodensitometry?
2C model: FM & FFM
What compartment model is DEXA?
3C: Bone density, FFM and FM
Osteoporosis
A condition in which the body's bones become weak and break easily.
Bioelectrical Impedance Analysis (BIA)
A method of assessing body composition by running a low-level electrical current through the body, measuring the impedance to that current (FM), estimates total body water (FFM)
What principle is hydrodensitometry based on?
Archimedes' principle: "A body immersed in water is subjected to a buoyant force that results in a loss of weight equal to the weight of the displaced water" - Measures body volume and then you can calculate body density
Body Mass Index (BMI)
Based on anthropometric measures- height and body mass
What principle is plethysmography based on?
Boyle's Law (air displacement)
CT/MRI scans
Cross-sectional imaging of the whole body, can determine visceral fat
Indirect estimation techniques
DEXA, Bod Pod, MRI/CT scan, Hydrostatic weighing
Doubly indirect method
Derived from an indirect method, equation based on indirect, more error is possible
Indirect method
Derived from the direct method, predicting % body fat
Estimation techniques for body composition
Direct, indirect, & doubly indirect
What are some benefits associated with BMI?
Largely population based and has been used to look at prevalence of overweight and obesity in US adults for decades
Osteopenia
Loss of bone mineral density which causes bones to become weak
What equations are used to calculate body fat from body density?
Siri equation (most common, for general population) Brozek equation (used in extremes, highly lean/overweight)
Doubly Indirect estimation techniques
Skinfolds, BIA, Ultrasound
Distribution of body fat is important True or False
True
Component-based analysis
Two-compartment (2C) model: - Fat Mass (FM) & Fat Free Mass (FFM) - Widest application to body composition analysis - Easy to perform and convenient - Limited by assumptions: Water & mineral contents of the body remain constant, Density of FFM is similar among individuals Multi-compartment (3C, 4C & 5C) models: - partitions body mass into more than 2 compartments - requires more measures -> more difficult to assess
What are consequences of having low body fat?
changes in bone structure and muscle mass - Osteoporosis - Osteopenia - Sarcopenia
Direct method
chemical analysis of the whole body or cadaver, true measure of body composition
Waist-to-Hip Ratio (WHR)
estimate of visceral obesity (fat surrounding organs) measures waist circumference (should be measured at top of iliac crest) & hip circumference
Property-based analysis
generally involves the measurement or estimation of a specific property: - body volume: hydrostatic weighting/air displacement plethysmography - total body water: BIA - x-ray absorption: DEXA/CT
Body composition can provide information about ____________
health status
Sarcopenia
loss of skeletal muscle
What are some issues associated with BMI?
relationship between BMI and body fat percentage is not linear BMI and body fat is different between women and men Age, sex, bone structure, fat distribution/muscle mass can affect accuracy of BMI
How do you calculate BMI?
weight (kg) / height (m^2)
Dual-Energy X-Ray Absorptiometry (DEXA)
x-ray used to determine body fat, fat distribution pattern, and bone density
