Body Composition - Lecture 18 Flashcards
What is the most common measure of Obesity?
BMI
BMI was not meant to measure obesity
It’s just a linear relationship between weight and height.
What do cut points indicate in terms of BMI
Indicates the risk of death depending on one’s BMI
What’s the correlation of BMI and Fat Tissue
Increased BMI = Increased Fat Tissue
How many classes of Obesity are there?
3 classes
BMI Class 1
30.0-34.9
Level of Risk in Class 1
High Risk
BMI Class 2
35.0-39.9
Level of Risk in Class 2
Very High Risk
BMI Class 3
≥40.0
Level of Risk Class 3
Extremely High Risk
Asian Decent
Cut Points are a bit lower for each classification
What two things are body mass (composition) divided into
Fat and Fat-Free Mass
What is Fat-Free Mass?
Everything not including fat.
Fat Mass
All Fat Tissue in the body
What are ways to measure fat since BMI isn’t a way
Densitometry, Dissection, MRI, CT, DEXA, BIA, Ultrasound, Anthropometry, Skinfold Measures
Densitometry
Measure of how dense one is through weight/volume
What would more fat mass indicate?
Lower density; floats to top
Fat free mass indicator in densitometry
More lean muscle and dense bones would mean sinking to bottom. (Less fat mass)
2 ways in measuring density
Hydrostatic & Air Displacement
Hydrostatic Method
Looking at weight differences when in water compared to air
Air Displacement method
Changing the volume air in bodpod and then looking at the difference in pressure change to determine volume & calculate density.
Best Technique for Fat Mass measurement
Dissection; through prediction as humans can’t be sliced
Visible Human Project
Project showing that imaging techniques are like cutting you into multiple pieces and measuring body composition.
MRI
Able to check fat mass via “cutting” into pieces and putting it in a 3D image.
What does an MRI check when cutting a cross section
How much bone and fat is in that section.
Why is MRI considered the gold standard of body composition assessment
It gets the job done pretty accurately, but it’s very expensive.
Purpose of magnets in MRI
changes the spin of H+ ions in the cross sectional area to produce the image we see.
CT Scans
Unlike using magnets, it uses radiation to get clear precise images
Pro of CT
Gets clear image
Con of CT
Body absorbs radiation
Dual Energy X-Ray Absortiometry (DEXA)
Used as a bone density machine; often checks for osteoporosis.
Check for high bone density and low bone density
Shoots beams of radiation and high bone density means beam does not pass through, but low density means it easily passes through
What’s an indicator of osteoporosis?
Low bone density
What is one pro of DEXA?
Cheaper than CT and MRI
Can DEXA be used for only bone density measurement?
Can also measure body composition (fat mass and fat-free mass) through same methods.
Bioelectrical Impedence Analysis (BIA)
Shoots electrical currents in body and is sent to the receiver to determine how well the body conducts electricity.
What does the hardly conducting electricity indicate?
High fat mass (not much water in fat mass)
What does a lot of conduction indicate?
High fat-free mass (contains water)
What can affect the BIA test?
Hydration status, model of device that is used may not tell you accurately.
Ultrasound
Sends sound waves through tissue and sends a signal back producing an image
Anthropometry
Measures fat in different parts like the waist using measuring tape
Pro of Anthropometry
Very very cheap.
Skinfold Measures
Measures skin and fat thickness at various sites and predicts %BF
Common sites for Anthropometric Measure
There are many sites, but it depends on what you’re interested in looking at. (Looking at functionality in the thigh of someone who fell down the stairs.
How was %BF predicted with skinfold equations?
Taking skinfolds from corpse and look at how it predicts total fat mass.
Does the %BF prediction with skinfold equations still apply in this day and age?
No; hydrostatic weighing and things like MRI give us a better prediction.
What does the Durnin equation show?
The sum of 4 skinfolds show that females have a higher %BF than males.
What are other differences in the %BF table?
Older people have more body fat than younger
Overall what are factors influencing skinfold fat equations?
Sex and Age
Finding average %BF
Takes fat measures and compares it back to different classifications of weight (underweight - Obese class 3)
What are the reasons that assigning a percentage for Body Fat based on BMI doesn’t always work?
- What’s quote on quote normal will change
- Most of these comparisons use BMI as a reference; BMI is not an indicator of fat tissue.
How can you track average %BF accurately?
Stick to using the same device and method to measure
Why are recommended values of %BF varying?
Depends on the equation used to determine. That’s why sticking to one method and machine is better.
Fat but Fit Paradox
Those with high BMI and adipose tissue that also have a high VO2Max, that diminishes the mortality risk related to obesity.
