Lecture 2 Flashcards
Measuring body composition I
Two-component model
Fat mass (FM) + fat-free mass (FFM)
Three component model
Fat mass (FM)+ fat-free mass (FFM)
Fat free mass (FFM)=
- Bone mineral content (BMC)
- Bone-free fat-free mass
Weight alone can be very misleading
Doesnt tell us how much of the weight of fat free mass and where is it stored
Depends on how much muscle
Why measure body composition
-Health
-Sports performance
-Monitoring growth
-Assessing response to intervention
-Creation of reference values
-Population monitoring
Total Body Composition
% fat= (FM/body weight) x 100
%FFM= (FFM/body weight) x 100
Regional Body composition
Is fat stored primarily in the central or peripheral regions?
Health risks of obesity depend on …
Regional fat distribution as well as total body composition
There are two types of bodies
Central (apple)= Android
Peripheral (Pear)=Gynoid
Which one of the two body types is the most concerning for health
Central
Central adiposity increases health risks such as?
type 2 diabetes
Coronary heart disease
Cardiovascular disease
Arthritis
Central fat=visceral
Intra abdominal
Subcutaneous
under the skin fat
What fat increases health risks the most
visceral fat
When measure regional fat distribution ideally want to measure
Visceral fat
Visceral fat is more
metabolically active
Many different methods some measure … and others measure …… and some measure both
Total body composition
Regional body composition
Two component model explanation
measure either FM or FFM and calculate the other from total body weight
Assume composition of FFM is constant which is
Not always true- there are always going to be an issue with what method you use
Three main types of approach for two-component model
1) Densitometry
2) Electrical resistance of the body
3) External measurement
Densitometry
1- Underwater weighing
2- Air displacement plethysmography
Electrical resistance of the body
Bioelectrical impedance analysis
External measurement
Anthropometry
Density
Mass/volume
Equations have been developed that allow us to calculate ………… then FFM
% fat from total body density
FFM can then be calculated by difference
Densitometry- assumptions
-The density of fat free mass is constant
-The density of fat does not vary amoung people
-The water content of fat free mass is constant
-The proportion of bone to fat free mass is constant
Underwater weighing
The amount that has been displaced
You breath out as much as possible (you get emersed for 7 seconds and then you have to do this for about 4 to 12 times)
Underwater weighing: Calculation 1
Body volume
Mass(air) -mass(water)-RV-100 / body volume
Underwater weighing: Calculation 2
Body density
Mass(air) / body volume
Underwater weighing: Calculation 3
% body fat
=((4.95 / body density)- 4.50) x 100
Underwater weighing: Advantages
-Gold standards
-Accurate
-2% error
Underwater weighing: Disadvantages
-Density of FFM not necessarily uniform
-Do 4-12 times
-Not suitable for all
-Breathing apparatus to measure lung volume
-Bulky equipment
Underwater weighing is known as a …
“Gold standard”
Air displacement plethysmorgraphy
-For example: the BOD POD
-Similar principle to underwater weighing
-Except calculate displaced air rather than displaced water when person is in and out of chamber
-Practical advantages compared with underwater weighing
Bioelectrical impedance analysis
Body conducts electricity through FFM
Pass weak current through body and measure impedance (resistance + reactance) to current
Bioelectrical impedance analysis: Validity can be impacted by:
-Hydration status
-Recent physical activity
-Consumption of food/drink
-Menstrual status
-Body position
Bioelectrical impedance analysis: Good practice
-Avoid alcohol & vigorous exercise 24-48 hours before
-Measure >-2 h after eating and within 30 min of voiding
-Subjects lie down, with limbs not touching body
Improve measurement by adding sex and age
Practice the calculations
1) Total body water
2)Fat free mass
3)Fat mass
4)Body fat %
Bioelectrical impedance analysis: Advantages
-Simple
-Cheap
-Portable
-Suitable for all ages
Bioelectrical impedance analysis: Limitations
-Need to be fasting
-Control recent activity & hydration status
-Need appropriate equation for your participants
Anthropometry
-Most widely used method
-BMI, skinfolds, circumferences, breadths
Anthropometry: Interpret by
-Comparing results with reference data: percentiles or standard deviation score (Z-score)
-Using cut offs that relate to risk (morbidity, malnutrition)
Anthropometric Reference Data
Data need to be developed from group representative of healthy population-need to be specific (age, gender, ethnicity)
Often presented as percentiles
Percentiles
Describe the position of the measurements in relation to the measurements in relation to the measurements for a population
NB: At the 50th percentile 50% of the population are below that value and 50% are above
Anthropometry: Advantages
-Simple
-Safe
-Noninvasive
-Cheap
-Portable equipment
Commonly used for large studies
Anthropometry: limitations
Less accurate so less sensitive to change
Potential sources of error:
- Measurement error
-Variation in tissue composition
-Assumptions may not be valid in disease states or obesity
