Body Composition – Questions With Complete
Solutions
Components of total body mas ✔️Ans - 1. Adipose
2. Lean body mass (muscle, bone, extra-cellular, water, other)
Measures of absolute body components (to separate adipose from lean
body mass) ✔️Ans - 1. Dilution
2. Densitometry
3. Impendence
4. Anthropometric measures (skinfolds, circumference measures, height
and weight)
Principle of dilution ✔️Ans - Calculate total body water to derive lean
body mass
Assumption of dilution ✔️Ans - Water makes up 73% of lean body mass
and no water in adipose
Dilution procedure ✔️Ans - 1. Consume known amount of substance
(radioactive)
2. Wait for mixing
3. Measure concentration of substance in urine
4. Lean body mass = (total body water/0.732)
Disadvantage of dilution ✔️Ans - Requires drinking radioactive
substance and measuring urine: not feasible for large studies
Densitometry ✔️Ans - Underwater weighing
Principle of densitometry ✔️Ans - Body composition estimated using
body density (density=mass/volume)
Assumption of densitometry ✔️Ans - Fat tissue is less dense than fat-free
tissue, uses standard equations to calculate % body fat assuming constant
density for lean body mass
2 compartment model of densitometry ✔️Ans - fat and fat-free mass
, Which method is considered the gold standard for % body fat? ✔️Ans -
Densitometry (underwater weighing)
How Densitometry works ✔️Ans - 1. Measure body weight in air and in
water and calculate the difference (loss of weight in water = the weight of
the volume of water displaced)
2. Use known density of water to calculate the volume of water displaced
(=volume of the body)
3. Based on the volume and weight of the body, you can calculate its density
4. Standard formula: density=body fat%
Densitometry using 'BOD POD' ✔️Ans - Use of air pressure instead of
underwater weighing to calculate body volume. Uses Boyle's law: pressure
and volume vary inversely with one another. Therefore, monitoring
pressure changes in a closed chamber allows one to calculate volume.
Limitations of densitometry ✔️Ans - 1. 2-compartmental model:
assumes that the components that make up the fat-free mass (water,
minerals, protein) are relatively constant from person to person)
2. Labor intensive
3. No information on fat distribution
Principle behind impedance and conductance to measure adiposity ✔️Ans
- Lean body mass conducts electricity better than fat
What is conductance? ✔️Ans - Pass body through a large coil and
measure difference between impedance when coil empty vs. when subject
present
Limitations to conductance? ✔️Ans - 1. Expensive
2. Not portable
3. Not practical for large studies
What is impedance (BIA- bioelectrical impedance analysis) ✔️Ans - Pass
low-level electrical signals using electrodes placed on subject. The faster
the signal travels, the more lean mass.
Advantages to impedance ✔️Ans - 1. Inexpensive
Solutions
Components of total body mas ✔️Ans - 1. Adipose
2. Lean body mass (muscle, bone, extra-cellular, water, other)
Measures of absolute body components (to separate adipose from lean
body mass) ✔️Ans - 1. Dilution
2. Densitometry
3. Impendence
4. Anthropometric measures (skinfolds, circumference measures, height
and weight)
Principle of dilution ✔️Ans - Calculate total body water to derive lean
body mass
Assumption of dilution ✔️Ans - Water makes up 73% of lean body mass
and no water in adipose
Dilution procedure ✔️Ans - 1. Consume known amount of substance
(radioactive)
2. Wait for mixing
3. Measure concentration of substance in urine
4. Lean body mass = (total body water/0.732)
Disadvantage of dilution ✔️Ans - Requires drinking radioactive
substance and measuring urine: not feasible for large studies
Densitometry ✔️Ans - Underwater weighing
Principle of densitometry ✔️Ans - Body composition estimated using
body density (density=mass/volume)
Assumption of densitometry ✔️Ans - Fat tissue is less dense than fat-free
tissue, uses standard equations to calculate % body fat assuming constant
density for lean body mass
2 compartment model of densitometry ✔️Ans - fat and fat-free mass
, Which method is considered the gold standard for % body fat? ✔️Ans -
Densitometry (underwater weighing)
How Densitometry works ✔️Ans - 1. Measure body weight in air and in
water and calculate the difference (loss of weight in water = the weight of
the volume of water displaced)
2. Use known density of water to calculate the volume of water displaced
(=volume of the body)
3. Based on the volume and weight of the body, you can calculate its density
4. Standard formula: density=body fat%
Densitometry using 'BOD POD' ✔️Ans - Use of air pressure instead of
underwater weighing to calculate body volume. Uses Boyle's law: pressure
and volume vary inversely with one another. Therefore, monitoring
pressure changes in a closed chamber allows one to calculate volume.
Limitations of densitometry ✔️Ans - 1. 2-compartmental model:
assumes that the components that make up the fat-free mass (water,
minerals, protein) are relatively constant from person to person)
2. Labor intensive
3. No information on fat distribution
Principle behind impedance and conductance to measure adiposity ✔️Ans
- Lean body mass conducts electricity better than fat
What is conductance? ✔️Ans - Pass body through a large coil and
measure difference between impedance when coil empty vs. when subject
present
Limitations to conductance? ✔️Ans - 1. Expensive
2. Not portable
3. Not practical for large studies
What is impedance (BIA- bioelectrical impedance analysis) ✔️Ans - Pass
low-level electrical signals using electrodes placed on subject. The faster
the signal travels, the more lean mass.
Advantages to impedance ✔️Ans - 1. Inexpensive
