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HUNT242 > Lecture 3 > Flashcards

Lecture 3 Flashcards

Measuring Body composition II

1
Q

Anthropometry -BMI

A

Body Mass Index (BMI)= weight (kg) / height (m)^2

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2
Q

BMI Advantages

A
  • Easy, quick, non-invasive
    -Correlates with percent body fat at group level
    -Useful for individuals- with additional information
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3
Q

BMI: limitations

A

-Doesn’t tell you what weight is measuring
-High BMI could be high lean, fat, oedema

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4
Q

Anthropometry- Mid-upper-arm circumference

High income countries

A

Decrease can reflect reduction in muscle or fat (or both)

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5
Q

Anthropometry- Mid-upper-arm circumference

Low income countries

A

-Subcutaneous fat small so MUAC changes parallel changes in mucle mass
- Diagnosis of Protein Energy malnutrition

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6
Q

Mid-upper-arm circumferance =Can be used to calculate muscle estimates

A

-Mid-upper-arm muscle circumference
-Mid-upper-arm muscle area

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7
Q

Anthropometry -Skinfolds (what is used)??

A

-Calipers measure fold of skin & underlying fat

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8
Q

Calipers: Data used

A

-By comparing to percentiles
-To calculate % fat using equations

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9
Q

Common skinfolds

A

-Triceps
-Biceps
-Subscapular
-Suprailiac
-Thigh, calf, abdomen

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10
Q

Skinfolds: Advantages

A

-Simple
-Cheap
-Can be precise and accurate

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11
Q

Skinfolds: Limitations (assumptions)

A

-Constant skin and subcutaneous fat compressibility
-Constant skin thickness
-Chosen sites are good estimate of total fat
-Subcutaneous fat represents constant proportion of fat in every person

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12
Q

Oedema

A

Extra cellular fluid building uo in the skin

  • leaves a dent
    -Wet beri beri
    -Low income countries this can occur due to a lack of nutrition
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13
Q

Why cant you measure fat mass with someone who has oedema

A

You wont be able to take a useable measurement because it wont be able to measure your exact fat mass because you have to much fluid in the way

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14
Q

Three-component model

A

Fat mass(FM) + Fat-free mass (FFM)

Fat free mass
- Bone mineral content
-Lean soft tissue

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15
Q

Dual-energy X-ray Absorptiometry (DEXA)

A

-Medical imaging technique
- Small amount of radiation used to measure lean mass, fat mass and bone mineral content

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16
Q

Dual-energy X-ray Absorptiometry (DEXA)

Principles

A

-Dense tissues (e.g bone) absorb more X-rays, less dense tissue (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

17
Q

DEXA:advantages

A

-Accurate (2% error)
-Precise (grams FM, lean mass, BMC)
-Suitable for almost all ages
-Relatively quick

18
Q

DEXA: Disadvantages

A

-Expensive
-Size limits
-Requires trained technician

19
Q

Four main types of approach for regional body composition

A

1-Computed tomography (CT)
2-Magnetic resonance imaging (MRI)
3-DEXA- Calculated estimate
4-Anthropometry- circumferences

20
Q

Computed Tomography

A

-Medical imaging technique
-Rotating X-ray tube and detectors -> detailes cross-sectional images

21
Q

Computed tomography is used to measure

A

Lean mass, fat mass and bone mineral content

  • Can also discriminate between visceral and subcutaneous fat
    -“Gold standard”
22
Q

Computed Tomography: advantages

A

-“Gold standard”
-Accurate
-Measures visceral fat

23
Q

Computed Tomography: limitations

A

-Expensive
-Higher levels of radiation than DXA so limitations on use

24
Q

MRI

A

-medical imaging technique
-Strong magnetic field & radio waves -> detailed cross sectional images

25
Q

MRI used to measure

A

Lean mass, fat mass and bone mineral content
-Can also discriminate between visceral and subcutaneous fat
- Different tissues emit different radio waves when H atoms align by magnetic field

26
Q

MRI: Advantages

A

-Very accurate
-No radiation, so multiple scans on same person possible
-Measure visceral fat

27
Q

MRI: Limitations

A

-Expensive
-Slow
-Strong magnetic field

28
Q

DEX- calculated estimate

A

-Can measure regions
-But cant discriminate between visceral and subcutaneous fat

Estimate visceral fat from an automated image-processing algorithm using raw 2D images from DXA

29
Q

Anthropometry- circumferences

A

Waist (proxy for central fat)
Hip (proxy for peripheral fat)
Calculate waist:hip ratio (WHR)

30
Q

Calculate waist:hip ratio (WHR)
BUT ……

A

Many now consider that waist circumference alone is better indicator of visceral fat

31
Q

Calculating abdominal visceral fat level from body composition

A

To evaluate the merit BMI, % body fat, waist circumference and WHR as predictors of abdominal visceral fat level

32
Q

what was the best measure for AVF

A

waist circumference was the best overall indicator of abdominal visceral fat level- with correlation coefficients >-0.75 for younger and older women and men. WHR was a poor measure of AVF especially in women and should not be used as a surrogate measure of visceral obesity

33
Q

Circumferences: Advantages

A

simple

34
Q

Circumferences: Disadvantages

A

-Not direct measure of visceral fat
-Difficult in very obese

35
Q

Body fat % Obese Men

A

> 25

36
Q

Body fat % Obese Women

A

> 35

37
Q

when measuring regional body fat and its relationship to health we ideally want a measure of

A

Visceral, central fat

HUNT242 (23 decks)

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