Lecture 3

Question 1

Anthropometry -BMI

Answer 1

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

Question 2

BMI Advantages

Answer 2

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

Question 3

BMI: limitations

Answer 3

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

Question 4

Anthropometry- Mid-upper-arm circumference

High income countries

Answer 4

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

Question 5

Anthropometry- Mid-upper-arm circumference

Low income countries

Answer 5

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

Question 6

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

Answer 6

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

Question 7

Anthropometry -Skinfolds (what is used)??

Answer 7

-Calipers measure fold of skin & underlying fat

Question 8

Calipers: Data used

Answer 8

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

Question 9

Common skinfolds

Answer 9

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

Question 10

Skinfolds: Advantages

Answer 10

-Simple
-Cheap
-Can be precise and accurate

Question 11

Skinfolds: Limitations (assumptions)

Answer 11

-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

Question 12

Oedema

Answer 12

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

Question 13

Why cant you measure fat mass with someone who has oedema

Answer 13

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

Question 14

Three-component model

Answer 14

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

Fat free mass
- Bone mineral content
-Lean soft tissue

Question 15

Dual-energy X-ray Absorptiometry (DEXA)

Answer 15

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

Question 16

Dual-energy X-ray Absorptiometry (DEXA)

Principles

Answer 16

-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

Question 17

DEXA:advantages

Answer 17

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

Question 18

DEXA: Disadvantages

Answer 18

-Expensive
-Size limits
-Requires trained technician

Question 19

Four main types of approach for regional body composition

Answer 19

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

Question 20

Computed Tomography

Answer 20

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

Question 21

Computed tomography is used to measure

Answer 21

Lean mass, fat mass and bone mineral content

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

Question 22

Computed Tomography: advantages

Answer 22

-“Gold standard”
-Accurate
-Measures visceral fat

Question 23

Computed Tomography: limitations

Answer 23

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

Question 24

MRI

Answer 24

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

Question 25

MRI used to measure

Answer 25

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

Question 26

MRI: Advantages

Answer 26

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

Question 27

MRI: Limitations

Answer 27

-Expensive -Slow -Strong magnetic field

Question 28

DEX- calculated estimate

Answer 28

-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

Question 29

Anthropometry- circumferences

Answer 29

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

Question 30

Calculate waist:hip ratio (WHR) BUT ......

Answer 30

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

Question 31

Calculating abdominal visceral fat level from body composition

Answer 31

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

Question 32

what was the best measure for AVF

Answer 32

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

Question 33

Circumferences: Advantages

Answer 33

simple

Question 34

Circumferences: Disadvantages

Answer 34

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

Question 35

Body fat % Obese Men

Answer 35

>25

Question 36

Body fat % Obese Women

Answer 36

>35

Question 37

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

Answer 37

Visceral, central fat