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HUNT 242 > Lecture 3 - Measuring Body Composition > Flashcards

Lecture 3 - Measuring Body Composition Flashcards

1
Q

what are the advantages to BMI

A
  • easy, quick, non-invasive
  • correlates with percent body fat at group level
  • useful for individuals - with additional information
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2
Q

what are the limitations to BMI

A
  • doesn’t tell you what weight is measuring
  • high BMI could be high lean, fat, oedema
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3
Q

in high income countries mid upper arm circumference a decrease can reflect

A

a decrease can reflect reduction in muscle or fat (or both)

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4
Q

in low income countries mid upper arm circumference a changes show what and why

A

subcutaneous fat small so MUAC changes are parallel changes in muscles mass

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5
Q

in low income countries mid upper arm circumference can lead to diagnosis of

A

Protein Energy Malnutrition (PEM)

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6
Q

middle upper arm circumference can be used to calculate muscle estimates such as…

A
  • middle upper arm muscle circumference (MUAMC)
  • mid upper arm muscle area (AMA)
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7
Q

in what countries is mid upper arm circumference more useful than others

A

more useful in low income countries than high income ones

  • due to less subcutaneous fat so would show more changes in muscle mass
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8
Q

what is a skin fold

A

calipers measure fold of skin and underlying fat

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9
Q

data from skinfolds is used to

A

comparing to percentiles

or

to calculate % fat using equations

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10
Q

what are common skinfolds

A
  • triceps
  • biceps
  • subscapular
  • suprailiac
  • thigh, calf, abdomen
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11
Q

what are the advantages to skinfolds

A
  • simple
  • cheap
  • can be precise and accurate
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12
Q

what are the limitations / assumptions to skinfods

A
  • constant skin and subcutaneous fat compressibility
  • constant skin thickness
  • chosen sites are a good estimate of total fat
  • subcutaneous fat represents constant proportion of total fat in every person
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13
Q

what kind of technique is dual energy x-ray absorptiometry (DEXA)

A

medical imaging technique

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14
Q

how does the dual energy x-ray absorptiometry (DEXA) work

A

small amount of radiation used to measure lean mass, fat mass and bone mineral content

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15
Q

what are the principles of dual energy x-ray absorptiometry (DEXA)

A
  • dense tissues (e.g bone) absorb more x rays, less dense tissues (e.g fat) absorb less
  • detectors under the body measure intensity of X rays that have passed through
  • DEXA then generates a 2 dimensional image
  • software algorithms calculate body composition
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16
Q

what are the advantages to dual energy x-ray absorptiometry (DEXA)

A
  • accurate (2% error)
  • precise (grams FM, lean mass, BMC)
  • suitable for almost all ages
  • relatively quick
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17
Q

what are the limitations to dual energy x-ray absorptiometry (DEXA)

A
  • expensive (100-150 bucks per session)
  • size limits (some people may be too wide)
  • requires trained techniciain
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18
Q

what are the 4 main types of approach for measuring regional body composition

A
  1. computed tomography (CT)
  2. magnetic resonance imaging (MRI)
  3. DEXA - calculated estimate
  4. anthropometry - circumferences
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19
Q

what type of technique is computed technology

A

medical imaging technique

20
Q

how does computed technology work

A

rotating X-ray tube and detectors, gives detailed cross sectional images

21
Q

what is computed technology used to measure

A

lean mass, fat mass and bone mineral content

22
Q

what can computed technology discriminate between

A

between visceral and subcutaneous fat

23
Q

what is computed technology considered

A

“gold standard”

24
Q

what are the advantages to computed technology

A
  • “gold standard”
  • accurate
  • measures visceral fat
25
Q

what are the disadvantages to computed technology

A
  • expensive (more expensive than DEXTA)
  • higher levels of radiation
26
Q

what kind of technique is magnetic resonance imaging (MRI)

A

medical imaging technique

27
Q

how does magnetic resonance imaging (MRI) work

A

strong magnetic field and radio waves, gives detailed cross sectional images

28
Q

what is magnetic resonance imaging (MRI) used for

A

to measure lean mass, fat mass and bone mineral content

29
Q

what can magnetic resonance imaging (MRI) discriminate between

A

visceral and subcutaneous fat

30
Q

in MRI, different tissues emit

A

different radio waves when H atoms aligned by magnetic field

31
Q

what are the advantages to magnetic resonance imaging (MRI)

A
  • very accurate
  • no radiation, so multiple scans on same person possible
  • measures visceral fat
32
Q

what are the limitations to magnetic resonance imaging (MRI)

A
  • expensive
  • slow
  • strong magnetic field
33
Q

dual energy X ray absroptiometry (DEXA) - calculated estimate is lots cheaper than

A

CT or MRI scans

34
Q

dual energy X ray absroptiometry (DEXA) - calculated estimate can measure

A

can measure regions

35
Q

dual energy X ray absroptiometry (DEXA) - calculated estimate can not discriminate between

A

visceral and subcutaneous fat

36
Q

dual energy X ray absroptiometry (DEXA) - calculated estimate can estimate visceral fat from

A

an automated image processing algorithm using raw 2D images from DXA, this can be incorrect though

37
Q

in anthropometry waist circumferences are a proxy for

A

central fat

38
Q

in anthropometry hip circumferences are a proxy for

A

peripheral fat

39
Q

waist and hip circumference can be used to calculate

A

waist : hip ratio

40
Q

what do many now consider about waist circumference

A

many now consider that waist circumference alone is a better indicator of visceral fat rather than waist : hip ratio

41
Q

what are the advantages to using circumferences

A

simple

42
Q

what are the disadvantages to using circumferences

A
  • not direct measure of visceral fat
  • difficult in very obese
43
Q

what are the cutoffs for obese % body fat commonly used in diagnostic textbooks

A

men >25%

women >35%

44
Q

more accurate methods of measuring body composition are usually

A

more expensive or difficult

45
Q

choosing a method for measuring body composition will depend on

A

time, resources, cost and participants

HUNT 242 (14 decks)

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