Body Composition & Obesity

Question 1

What is BMI?

Answer 1

The most common measure of obesity
weight (kg)/ height (m^2)

Question 2

Limitations of BMI?

Answer 2

• Cannot distinguish different body composition
• not suitable for pregnancy
• shows that athletes who have high muscle mass have a high BMI however they have low body and no disease risks

Question 3

BMI Table

Answer 3

<18.5= underweight
18.5-25= healthy
25-30= overweight
>30= obesity

Question 4

2 compartment model

Answer 4

fat and fat-free mass (anything that is not fat like bone, muscles etc)

Question 5

3 compartment model

Answer 5

fat-free mass, bone mass and lean mass (fat and bone free)

Question 6

4 compartment model

Answer 6

better imaging

Question 7

8 techniques of assessing body fat

Answer 7

1. Densitometry
2. Skinfold measurements
3. Computed tomography (CT scan)
4. Magnetic resonance imaging (MRI)
5. Total body density (DXA)
6. Age, height and weight tables and weight prediction equations
7. Cadaver analysis
8. Bioelectric impedance analysis (BIA)

Question 8

Cadaver analysis

Answer 8

• takes direct measure of body tissue
• most accurate but impractical method
• used to validate the accuracy of other devices
• the majority of the data was taken from white males meaning there are limitations when seeing results for other ethnicities

Question 9

Densitometry

Answer 9

• density is proportional to fat-free mass (higher desity= higher FFM)
• volume of water/ air displaced= volume of the object

Question 10

Different methods of densitometry

Answer 10

• air displacement
• plethysmography (bod pod)
• hydro densitometry (underwater weighing)

Question 11

Bioelectrical impedance analysis

Answer 11

• fat and lean tissue have different conductance (fat tissue= insulator; no water, lean tissue- conductor; contains water)
• measures the impedance of electrical current (slower= more fat)
• equations to predict body fat
• can be affected by hydration status

Question 12

Skinfold measures

Answer 12

• takes mm measures of skin and fat thickness at various body sites
• subcutaneous
• sites: biceps, triceps, subscapular and supra-iliac, thigh, calf, abdomen

Question 13

Computed tomography

Answer 13

• 4C model
• consists of radiation hence not recommended
• expensive and time-consuming
• high-density tissues show up whiter (bone) and low-density tissues show up darker grey (fat)

Question 14

Magnetic resonance imaging

Answer 14

• 4C model
• magnet fields instead of radiation (preferred for research)
• expensive and time-consuming
• fat is lighter and bone is darker grey

Question 15

Dual-energy X-ray absorptiometry

Answer 15

• 3C model
• low dose of radiation
• less costly

Question 16

Why is fat in the waist region problematic?

Answer 16

as it is more associated with greater disease risk (more amount of fat affects the functionality of the organs in the area)

Question 17

Different types of fat?

Answer 17

subcutaneous- the one you can see
visceral- around the organs (more bad for you compared to the other)

Question 18

Does liposuction help with disease risk?

Answer 18

no, as it does not target the visceral fat

Question 19

Reasons for obesity increase?

Answer 19

• maladaptive lifestyle: energy imbalance
• food supply
• obesogenic environment
• no change in our genetics

Question 20

Obesity

Answer 20

60%-75% genetic
25%-40% environment

Question 21

Body mass in twins

Answer 21

monozygotic twins (identical twins) have a strong intrapair correlation of 0.66 in body mass compared to dizygotic twins (genetically unique) 0.26

Question 22

Adverse molecules secreted by adipocytes

Answer 22

• adipokines
• enzymes
• growth factors
• inflammatory mediators
• clotting factors