Lecture 3 - body composition

Question 1

What is body composition used for?

Answer 1

1. ) Nutritional status
2. ) Growth and development
3. ) Water homeostasis
4. ) Specific disease states

Question 2

How many levels of body composition?

Answer 2

5 levels

1. ) Atomic
2. ) Molecular
3. ) Cellular
4. ) Tissue
5. ) Whole body

Question 3

At the atomic level, what is the body compostion?

Answer 3

Oxygen - 43 kg / 61 %
Carbon - 16 / 23
Hydrogen -  7 / 10 
Nitrogen - 1.8 / 2.6
Calcium - 1.0 / 1.4
Phosphorus - 0.6 / 0.8

Question 4

At the molecular lebvel, body composition?

Answer 4

Water:
intracellular - 24 kg / 34 %
Extracellular - 18 / 26

lipds:
essential - 1.5 / 2.1
non essential - 12 / 17

Protein - 10.1 / 14.4
Minerals - 3.7 / 5.3
carbs - 0.5 / 0.6

Question 5

Body composition at the tissue level?

Answer 5

Muscle - 28 kg / 40 %
Adipose tissue - 15 / 21.4
Blood - 5.5 / 7.9 
Bone - 5 / 7.1
Skin - 2.6 / 3.7
Liver - 1.8 / 2.6

Question 6

What are the different methods to measure body compostiion?

Answer 6

1. ) direct method - componenets measured directly
2. ) Indirect methods - like determination of body protein from body nitrogen using conversion factor of 6.25 from N to prrotein
3. ) Doubly indirect methods - rely on a statistical relationship between easily measured body parameter and the component of interest, like assessment of skeletal muscle by creatinine excretion and the assessment of body fat by skin fold thickness

Question 7

What are the direct methods to measure body compostion?

Answer 7

Carcass analysis, IVNAA (measures elements)

Question 8

What are the indirect methods to measure body compostion?

Answer 8

Densitometry, 40K counting, CT/MRI scans

Question 9

What are the doubly indirect methods to measure body compostion?

Answer 9

Weight/height indices, skinfolds/ultrasounds, creatinine excretion 1g equivalent to 18-22 kg mucles

Question 10

What is a DXA scan?

Answer 10

When the body is scanned with x rays of two distinct energy levels.

Question 11

Attenuation of the tissues depends on what?

Answer 11

Depends on the chemical compostion and it is detected by photocells.

Question 12

In a DXA scan what does the software calculate?

Answer 12

Bone mineral content, bonemineral density, lean mass and adipose tissue mass.

Question 13

How does the measurement of the bicep skinfold work?

Answer 13

Skin folds from 4 sites usually. Accuracy is usually poor but it is the quickest and cheapest method. Use equations to predict body fat.