Body Composition: Basic Concepts and Techniques Flashcards
What does body composition mean?
- ratio of body fat to lean body mass
- amount of bone, fat, muscle tissue
5 levels of complexity for body composition models:
- atomic
- molecular
- cellular
- tissue-organ
- whole-body
Sum of components at each level =
body mass
_____ are the building blocks that form the whole body.
elements
6 elements that make up 98% of body weight:
- oxygen
- carbon
- hydrogen
- nitrogen
- calcium
- phosphorus
____ elements make up the other 2% of body weight.
44
6 major compartments of molecular level:
- water (intra + extracellular)
- protein (N containing compounds that form metabolic tissue in body)
- lipid
- carbohydrates (glycogen) = negligible
- bone minerals
- soft tissue minerals
Water is ____% of total body weight.
60%
Bone minerals and soft tissue minerals make up ____% of body weight.
5%
Label FM or FFM:
- lipid
- water
- protein
- carbohydrates
- soft tissue minerals
- bone minerals
- lipid (FM)
- water (FFM)
- protein (FFM)
- carbohydrates (FFM)
- soft tissue minerals (FFM)
- bone minerals (FFM)
Lean soft tissue consists of:
- metabolic tissue
- intracellular water
- extracellular water
Cellular level is comprised of:
- cells
- extracellular fluids (interstitial fluid and plasma)
- extracellular solids (bone minerals, collagen and elastic fibres)
BCM:
- body cell mass
- used to reflect the metabolic tissues and intracellular water
- site for most metabolic processes in the body
Tissue-organ level is comprised of:
- adipose tissue
- skeletal muscle
- bone
- visceral organs
- brain
- heart
Components of adipose tissue:
- subcutaneous
- visceral
- interstitial
- yellow marrow
Whole body level consists of:
- body size
- body shape
- exterior characteristics
- physical characteristics
The 5 level organization model of body comp provides the framework for understanding the different _____ available to assess body comp.
methodologies
Anthropometry is used to determine ____ ____ and _____.
- body size
- proportions
5 components of anthropometry:
- height
- weight
- BMI
- circumferences
- skinfold thickness
Why does height need to be accurate?
- used for energy requirement calculations
- used for BMI
- used for height/weight tables
- measure if possible
What is the most important anthropometric measure?
weight
Weight is related to ____, not ______.
- size
- composition
____ ____ are most accurate to measure weight. ____ status is found.
- electronic scales
- fluid
BMI evaluates ______ relative to _____ _____.
- weight
- health risk
BMI =
weight (kg)/height (m^2)
Interpretation of BMI:
- different values at age 65
- association with health risks
Why might BMI not tell the whole story?
- tables not separated by sex, age
- females have more fat at same BMI than men
- not a good measure in elderly
- can remain at same weight and still gain fat
Circumferences are used to estimate…..
- skeletal muscle mass
- body fat stores
Waist circumference correlates with ____ ____ ____.
visceral fat stores
Waist circumference is a useful index of ____ _____, _____ _____.
- abdominal obesity
- metabolic syndrome
Increased risk for ____ and ______ in overweight/obese individuals (males > ____ “, females > ____”).
- CVD
- type 2 diabetes
- 40”
- 35”
Waist to hip ratio estimates …..
distribution of subcutaneous and intra-abdominal adipose and muscle tissue
Bad waist to hip ratios (males > _____, females > ____) can possibly increase risk for ____ and ______.
- 1.0
- 0.8
- morbidity
- mortality
Advantages of body circumferences:
- mobile
- inexpensive
- fast, repeatable
- non-invasive
- no formal training
- useful for large samples
- anthropometrics and body comp values to which they relate are strongly linked to health
Disadvantages of body circumferences:
- limited accuracy
- training
- repeatability (WC and skinfolds)
Skinfold thickness is the measurement of ….
subcutaneous adipose tissue stores
Skinfold thickness is measured with _____.
calipers
Adipose stores vary with ____, _____, ____.
- age
- sex
- race
When doing skinfold thickness, using ____ ____ is more representative than only ____ _____.
- multiple sites
- one site
Skinfold thickness needs to be done by _____ _____.
trained individuals
Advantages of skinfold thickness:
- simple, fast, inexpensive, portable
- good reference data
- can be used with estimation equations
- best field technique for FM estimation (strongly correlate with % BF)
Disadvantages of skinfold thickness:
- includes skin and SAT
- affected by compressibility of SAT
- maximum jaw openings
- low precision
- training and experience essential
- poor correlation with FFM
BIA stands for:
bioelectrical impedance analysis
BIA estimates what 3 components of body comp?
- total body water
- FFM and FM
- body cell mass
How does BIA work?
- low level electrical current passes through the body
- FFM = electrical conductor
- FM = insulator
BIA is based on the relationship of ____ _____ to the ___ ____ of the body.
- body comp
- water content
FFM has high ____ and ____ content, it is ____ resistant to flow of the electrical current.
- water
- electrolyte
- less
Impedance:
opposition of a conductor to the flow of an alternating electric current (ie resistance to flow)
Advantages of BIA:
- safe
- potentially portable
- useful longitudinal observations
- variable instrument cost
Disadvantages of BIA:
- measurement sensitive to subject conditions such as hydration and recent activity
- instrument predictions may be population specific
Gold standard for body comp:
DEXA
DEXA stands for:
dual energy X-ray absorptiometry
DEXA is a ___ compartment:
- 3
- bone mineral density
- lean soft mass
- total and regional body fat
DEXA uses ___ ___ ___ and is ___ _____.
- low dose radiation
- non invasive
Exclusions for DEXA:
- pregnancy
- pt > 300 lbs
How does DEXA work?
low radiation x-rays of 2 different photon energy levels pass through the body and are identified by a photon detector that measures the amount of energy absorbed
ASM =
appendicular skeletal muscle
Advantages of DEXA:
- fast, non invasive
- convenience and comfort, to pre-test protocol
- direct quantification of body comp
- values for bone density and mass
- safe for serial measurement (low radiation)
- regional and whole body measurements
Disadvantages of DEXA:
- height and weight restrictions
- requires licensed technician
- operator error
- cannot compare data from different manufacturers’ machines
- not mobile
- high cost to purchase and operate
- cannot specifically discern skeletal muscle mass and quality (like CT/MRI)
Densitometry divides the body into ___ compartments:
- 2
- FM
- FFM
Densitometry measures ___ _____.
body volume (V)
Densitometry uses ____ to calculate ___ _____, because density =
- volume
- body density
- mass/volume
2 ways to do densitometry:
- hydrostatic weighing
- bod pod
Assumptions in densitometry:
- FM density = 0.901 g/ml
- FFM density = 1.10 g/ml
- densities of FM and FFM components (water, protein, mineral) are the same for all individuals
- proportion of the FFM components are constant within an individual
Hydrodensitometry:
- underwater weighing
- subject exhales upon submission in tank
In hydrodensitometry, body volume =
loss of weight in water
Archimedes principles:
- volume of submerged object = volume of water displaced
- weight - weight underwater = weight of water displaced
BV (hydrodensitometry) =
BW - UBW
BD (hydrodensitometry) =
BD = BW/BV
Advantages of hydrodensitometry:
- small error (equivalent to 2% BF)
- Well studied
- few safety concerns
Disadvantages of hydrodensitometry:
- operators require significant training
- measurement is difficult - not suitable for children, elderly, disabled
- people unwilling/unable to submerge in water
- not mobile
- residual volume is major source of error in density and %BF
Bod Pod is aka…
air displacement plethysmography
Bod pod estimates ____ from measured ____ ____. Subject seated in a _____ chamber.
- % BF
- body volume
- fiberglass
How does bod pod work?
- measures body volume by air displacement
- measures pressure changes with injection of known volume of air into closed chamber (pressure changes used to measure volume)
Body volume (bod pod) =
volume of air the subject displaces inside an enclosed chamber
Bod pod test procedures:
- subject sits inside bod pod chamber for 2 x 1 minute measurements
- bathing suit and swim cap
Pre-test protocol for bod pod:
- relaxed
- no eating, drinking, exercise 2 h pre-test
- void bladder
- no moisture on body, hair, swimsuit
- minimal or consistent facial hair
Advantages of bod pod:
- Fast, non-invasive
- Precise, simple to operate, rapid (minimal training required)
- Accommodates a variety of
populations: obese, elderly, children, disabled, infirm - No safety concerns
- Small error
- Somewhat mobile, may be suitable for field testing
- Suitable for patients up to 500 lbs, up to 7 ft tall
Disadvantages of bod pod:
- pre-test protocol
- lung volume must be estimated if measurement is difficult
- subject discomfort related to wearing bathing suit/tight fitting clothes, claustrophobia
- only one commercially available system
Only means of measuring level 4 (tissues and organs) is….
imaging
Imaging estimates tissue ____ and ____.
- quantity (area, volume, mass)
- quality (composition)
Methods of imaging:
- computerized tomography (CT)
- magnetic resonance imaging (MRI)
- ultrasound
CT:
- x rays attenuated as they pass through tissues
- different tissues = different density = different attenuation
- regional values, whole body (limited)
Advantages of CT:
- greatest accuracy
- high resolution, consistent values
- measured comp of internal tissues and organs
- detects regional shifts in body comp
- instruments widely available
Limitations of CT:
- high cost, limited access
- high radiation dose (repeated measures, special populations)
- CT imaging research in body comp typically accesses stored images from medical records
- requires technical skill
- limited to subjects with BMI < 35
MRI:
- magnetic resonance imaging
- generates a controlled magnetic field around the subject
- number of hydrogen nuclei of tissues is measured
- whole body and regional measurements
In MRI, tissues differ according to:
- number of hydrogen nuclei
- relaxation time (time to release energy)
- process repeated to map entire body
- estimates tissue quantity and quality
MRI advantages:
- high accuracy
- measured comp of internal tissues and organs
- detects regional shifts in body comp
- no radiation (repeated measures, most populations)
- whole body and regional analysis
MRI limitations:
- high cost, limited access
- limited to subjects with BMI < 35
Advantages of ultrasound:
- non-invasive/safe
- widely available
- useful for longitudinal monitoring
Disadvantages of ultrasound:
- technical skill required/protocol
- sensitive to severe altered water balance
4 techniques of body comp and which body comp of interest for each:
- BIA (FFM)
- DEXA (FFM, lean soft tissue, ASM)
- ultrasonography (skeletal muscle)
- CT (skeletal muscle)
Considerations of body comp:
- does it give you the info your client wants?
- does it measure the compartment of interest?
- $$, convenience, portable, frequency
- subject status (age, health, fitness, compliance)
- control of measurement variability
Variability in measurement could be due to:
- instrument error
- investigator error
- biological variability (activity, intake, etc.)
Why assess body comp?
- determine health status
- monitor changes in body comp (growth, aging, disease)
- evaluate efficacy of treatment (eg. exercise, diet, drug interventions designed to change body comp)
Skeletal muscle fundamental roles in human physiology:
- 40-50% of the body’s mass
- locomotion and movement
- blood flow to organs
- protection to vital organs
- regulator of whole body metabolism (storage site/consumer of AA and glucose) (endocrine organ –> myokines)
Low muscle mass can be a predictor of:
- shorter survival
- physical impairment/disability
- greater length of hospital stay
- need for rehab
- post op complications
- poor quality of life
- tumor progression/toxicity
