Body Composition

Question 1

Why measure body composition?

Answer 1

To determine normal/healthy growth
To evaluate nutritional status (under-nutrition, over-nutrition or specific
nutrient deficiencies)
To determine the effect of a nutrition intervention (diet or physical activity)
To assess the impact of a disease state

Question 2

Why is knowledge of body composition so important?

Answer 2

Health and Disease
✓ Performance
✓ Appearance
✓ Longevity

Question 3

what is meant by body composition

Answer 3

fat-free mass, fat mass, mineral, protein, water

Question 4

what is the Body Composition of Adult Male

Answer 4

72 kg = 42kg is water
Major component = water
Protein & and fat components are relatively small
Remainder = bone & other minerals

Question 5

expalin water in body composition

Answer 5

If we assume a fat mass of 12kg (17% of body weight)→
Fat-free mass (FFM) is 58kg (83% of body weight)
By far the biggest component of FFM is water (42 kg) which makes up 72.5% of FFM
Approximately
- 2/3 of water (28kg) is inside cells → intracellular fluid (ICF)
- 1/3 (14kg) is outside cells → extracellular fluid (ECF)
Body can lose up to 10% of its water without danger to life

Question 6

why do we need water

Answer 6

to lubricate joints, regulate body temp, help prevent constipation and protect body organs and tissues

Question 7

what is body compition in females vs males

Answer 7

females= less muslce 36% but more essentail fat 12%
males more muscle 45% but less essential fat 3%

Question 8

what is the essential fat in women used for

Answer 8

spleen, kidneys, spinal cord, liver and heart

Question 9

what makes up total body mass

Answer 9

lean body mass
(including essential fat) + adipose
tissue (storage fat)

Question 10

what are the % of body fat in males

Answer 10

15% is total
12% storage
3% essential

Question 11

what are the % of body fat in females

Answer 11

27% total fat
15% storage
12% essential

Question 12

expalin Gender differences in body composition

Answer 12

*In general women have greater proportion of body fat than men
*BUT absolute amounts are similar in both sexes at the same age and
increase with ageing
*Men have more muscle mass than women, women have approximately
2/3 of muscle mass of men

Question 13

explain Age differences
in body
composition

Answer 13

Lean body mass and fat-free mass increases to a
maximum in young adulthood then declines slowly
and linearly with age.
* This loss can be modified by physical activity and
cellular function.
* The variability in lean body mass between
individuals of a similar age and height is less than the
variability in body fat.
* The skeleton continues to grow till the late third
decade then the bone density declines at a linear rate
in men and pre-menopausal women but more rapidly
in post-menopausal women.

Question 14

what happens every year in adults

Answer 14

Because of the typical
reduction in physical activity,
each year the average adult
gains 0.7 kg of body fat and
loses 0.25 kg of lean tissue

Question 15

what is essential fat

Answer 15

• Essential fat = crucial for normal body functioning
  ▪3–5% of total body weight in males
  ▪8–12% of total body weight in females
  Consists of fat stored in:
  major organs (bone marrow, spleen, heart, lungs,
  intestines, liver, kidney)
  muscles
  central nervous system
  Important for childbearing and hormone-related functions
  (women have greater sex-specific needs)
  Required for normal physiological functioning → reducing essential fat below
  some minimal amount can impair overall health.
  Extremes in dieting (and exercise) can reduce essential fat stores

Question 16

what is non-essential fat

Answer 16

adipose tissue (storage fat)
▪12% of total body weight in males
▪15% of total body weight in females
Storage fat accumulates mainly in adipose tissue
This fat depot includes:
→ visceral fat
→ subcutaneous fat (common anatomic sites for subcutaneous fat include the triceps, subscapula, iliac, mid-abdomen, upper thigh)
Functions:
 insulation
 protection against trauma
 energy substrate
Men (12%) : Women (15%)
Distribution differs
 Men store fat………….?

Question 17

where is most adipose tissue stored?

Answer 17

lower trunk, upper trunk and thighs

Question 18

how do we calculate fat free mass

Answer 18

Fat Free Mass (FFM) → body mass devoid of all extractable fat
(i.e.) FFM = Body mass - fat mass

Question 19

how do we calculate lean body mass

Answer 19

Lean Body Mass (LBM) = FFM + essential fat
- Men → LBM includes 3% essential fat
- Women → LBM includes 12% essential fat

Question 20

what was the 2 compartment model

Answer 20

Assumption → the body is composed
of Fat and Fat Free Mass

Question 21

how do we assess body composition

Answer 21

Anthropometry
◦Bioelectrical impedance
◦Densitometry
- hydrostatic (underwater weighing)
- air displacement

Question 22

what are the Anthropometric assessment of body composition

Answer 22

✓Body Mass Index (BMI)
✓Body Circumferences
✓Waist-Hip ratio (WHR)
✓Skinfolds

Question 23

what are the Advantages of using BMI

Answer 23

inexpensive, simple to preform, can apply to large scale populations, good for public health recommendations

Question 24

explain risk based on BMI

Answer 24

Even though the risk for
premature illness and death is
greater for those who are
overweight, the risk also
increases for individuals who
are underweight

Question 25

What are the limitations of BMI

Answer 25

BMI lacks accuracy when estimating % fat of individuals
Does not consider the quality of weight (i.e.) fat vs lean
BMI of 25 or 30 does not correspond to the same % fat at
different ages
Ethnic group differences

Question 26

Explain Body Fat Distribution and Chronic Disease

Answer 26

Location (as well as the amount) of fat is important
to health
People who gain weight in
the abdominal area = “apples”
↑ disease risk
People who gain weight
in the hip area= “pears”

Question 27

What are the Disease risk according to waist-to-hip ratio

Answer 27

Predicts disease risk according to “apple” or “pear” shape
Waist circumference → level of the umbilicus
Hip circumference → largest circumference around the buttocks

Question 28

Explain skinfold thickness

Answer 28

Based on the principle that approximately half of the body’s fatty tissue is directly beneath skin
Reliable measurements of this tissue give an indication of percent body fat
Measurement:
Pressure calipers
Right hand side of body
Typically 4 sites (summed)
% fat is estimated from total mm

Question 29

What is Bioelectrical
Impedance

Answer 29

Resistance to the flow of an electrical current
through the body is related to total body water
(72.5% FFM)
(i.e.) fatty tissue is a less-efficient conductor of
an electrical current
Sensor electrodes are applied to the skin and a weak
(non detectable) electrical current is transmitted
through the body
Resistance to the flow of the current is measured and
used to estimate body fat, lean body mass, and body
water
Accuracy is similar to skinfolds, but affected by
hydration state

Question 30

what are the Principles of densitometry

Answer 30

Based on the 2-compartment model of body composition (i.e.) body weight is the sum of FAT and FAT FREE
MASS
Assumed that the density of each compartment is known and constant
Typically:
Density of fat = 0.9 kg/l
Density of fat-free mass = 1.1 kg/l (Siri, 1956)
Body Density = mass of the body/body volume
% Fat = 4.95 – 4.5 x 100
where d = body density
d

Question 31

what is Hydrodensitometry

Answer 31

One of the oldest methods of measuring body composition
Almost all other indirect techniques have been validated
against hydrostatic weighing
▪ Known as underwater weighing
▪ The weight of the subject is first measured in air and then
while totally immersed in water from which body volume is
calculated
Correction made for volume of air in:
▪lungs (either directly measured or prediction equations) and
▪Gut (standard 100ml is assumed for gut volume)

Question 32

what are the drawbacks of hydrodensitometry

Answer 32

Time consuming
Not feasible to test a large number of people
Requires measurement of lung and gut volume (if unknown, can be
estimated)
Difficult to perform on the aquaphobic

Question 33

what is the - Air Displacement (Bod Pod)

Answer 33

Individual sits inside small chamber
Computerized pressure sensors determine the amount of air
displaced by the person
Body volume is calculated by subtracting the air volume with the
person inside the chamber from the volume of the empty chamber
(air in the lungs is taken into consideration)
Body density and percent body fat are then calculated
Less cumbersome to administer
Takes only about 5 minutes

Question 34

what are the Research/medical facility techniques for assessing body composition

Answer 34

Dual energy X-ray absorptiometry (DEXA)
◦Magnetic resonance imaging (MRI)
◦Computed tomography (CT)
◦Total body electrical conductivity (TOBEC)

Question 35

what is Dual-energy X-ray absorptiometry (DXA)

Answer 35

Frequently used by research and medical facilities
Considered by many as the gold standard
technique for body composition assessment
Uses low-dose beams of X-ray energy
Measures fat mass, fat distribution pattern, and
bone density
Procedure is simple; takes only 15 minutes to
administer

Question 36

what is the right method to choose

Answer 36

There is no “best” method for measuring body composition in living subjects
Every method has errors
Some methods require expensive laboratory equipment (e.g.) DXA and could not be used in
community studies