Anthropometry and body composition Flashcards
What is BMI a good estimate for?
People with same BMI can have different body fat percentages. Good estimate for risk, not a good estimate for body composition.
Lean body mass =
Fat-free mass
(Total body mass - fat)
Lean soft tissue mass =
Lean body mass - bone
Appendicular =
Limbs
What do you get when you break down the body into the atomic level?
Oxygen + carbon + hydrogen + N & other elements
What do you get when you break down the body into the molecular level?
Lipid + water + protein + mineral + carbohydrate residue
(= FM (lipid) + FFM)
What do you get when you break down the body into the cellular level?
Body weight = cell mass + ECF + ECS
What do you get when you break down the body into the functional/tissue-organ level?
Adipose, bone, muscle, organ
What is the difference between direct vs indirect methods?
-> Direct methods: can accurately measure a component on atomic, molecular, cellular, tissue or whole body level
-> Indirect methods rely on rules and constants derived from direct methods.
What can you use to measure total body K?
Whole body K (potassium) counting (not used much)
- Of total body potassium, a fixed fraction is radioactive.
- If you know how much radioactive potassium there is, you can estimate total body K
- Fixed relationship between intracellular fluid (FFM) and total body potassium
Why is precision more valued than accuracy?
- May be optimal for measures of change in body composition, rather than absolute masses
- Lack the quality to be useful for individual assessment but work well in population studies
What is DEXA?
Dual Energy X-ray Absorptiometry:
Sending two x-rays which are absorbed differently by bones and soft tissues
> Measures bone mineral (direct) but also fat mass and lean mass (indirect)
What are advantages of DEXA? What types of studies is it moslty used?
- Regions of interest can be identified (e.g. abdomen, appendicular)
- Very low radiation exposure (less than sun exposure)
- Very precise
- Mostly used in research studies
Disadvantages of DEXA?
- Very expensive
- not easily portable
What is BIA? It is based on what principle?
Bio-impedance Analysis (BIA) = resistance of a body when an alternating current is applied.
> Based on differences in electrical conductivity (geleidbaarheid) (impedance) of body compartments (related to water content)
In what setting is BIA mostly used? What does it measure?
- Clinical setting
Measures TBW and ECW
-> Indirect estimate of body composition (FFM: no water in fat)
When can you not use BIA?
In situations in which hydration is different from the average value: pregnancy, critically ill or dehydratation
BIA estimates of body composition are dependent on..
The numerous equations, which are not publicly shared and often generic. However, ranking will be relatively stable
Errors of the BIA method are dependent on..
Device, operator, subject, measurement procedure, environmental conditions
What happens with isotope dilution?
A tracer (usually 2H2O) is used to measure TBW or ECW.
- Participant ingests water dose containing low amounts of 2H2O
- TBW or ECW can be clculated with C1 x V1 = C2 x V2 equilibrium
What are assumptions of isotope dilution? (= doubly labeled water)
- Tracer is (equally) distributed in body water compartments only
- Rate of equilibrium of the tracer is rapid
- Neither tracer nor body water is metabolised during time of equilibration
hydration of FFM = ?
73% (0.73)
How does the D3-creatine dilution technique work and what is it measuring?
- Ingesting a 30 mg dose D3 creatine
- Collecting morning urine sample (3–6 days) later - Measure D3-creatinine, unlabelled creatinine, and creatine
-> to determine total body creatine pool size and thus skeletal muscle mass
What is densitometry ? What are two techniques to measure this?
- Measurement of FM and FFM from body volume, because they have different densities.
(direct) measurement of body volume:
> Under water weighing
> Air displacement plethysmography
Not very nice for subjects.
What formula can be used to calculate FM?
Siri’s formula
What does siri’s formula look like for FM and BF%?
FM = 4.95BV - 4.50BM
BF% = 495/D-450
BV = body volume
BM = body weight
D = density
What is the added value of multiple component models?
If you can measure more, you can improve the quality of your assumptions (closer to the truth, but you will need more sophisticated machines etc)
What does the four comp model exist of ?
Fat, water, protein and bone mineral
What measures are needed for the 4 comp model?
- Densitometry (body volume to measure FM and FFM) and
- Hydrometry (isotope dilution) and
- DEXA
Assumption for 4 comp model?
Constant bone mineral content to non-osseous mineral content ratio
Order from 1 (highest) to 10 (lowest) estimation of body composition and costs and in a reverse manner the practical applicability with the following techniques:
- 3CM
- 4CM
- Densitometry (UWW/podypod) (clinical/lab)
- Anthropometry (field)
- DEXA
- Skinfolds
- BIA (field)
- Isotope dilution (field)
- Hydrometry (isotope, BIA) (clinical/lab)
- 3D imaging (CT/MRI)
- 4CM
- 3CM
- DEXA
- Densitometry (UWW/bodpod) (clinical/lab)
- Hydrometry (isotope, BIA) (clinical/lab)
- 3D imaging (CT/MRI)
- Anthropometry (field)
- BIA (field)
- Isotope dilution (field)
- Skinfolds
When is a technique doubly indirect?
When regression equations have to be used. (e.g. BIA or skinfold estimated body fat%)
So, what do the following techniques measure?
-DEXA
-BIA
-Densitometry
-Isotope dilution
- DEXA: Bone density (direct), FM and FFM
- Isotope dilution: Measurement of total body water TBW or ECW, FM +FFM indirect
- Densitometry: Measurement of FM and FFM from body volume (indirect)
- BIA: TBW (total body water) and ECW (extra cellular water), indirect body composition
