Body Composition Flashcards
Why measure body composition?
As an indicator of health status, to help favor optimal performance, to monitor changes, and to evaluate efficacy of treatments.
Excess fat is associated with many diseases, but the association is not perfect.
What is fat mass (FM)?
All extractable lipids from adipose and other tissues in the body.
What is fat-free mass (FFM)?
All residual, lipid-free chemicals and tissues.
aka. Fat free body (FFB)
What are essential lipids/fats?
Compound lipids (phospholipids) needed for cell membrane formation.
Define lean body mass (LBM).
Fat-free mass (FFM) plus essential lipids.
What is relative body fat (%BF)?
Fat mass expressed as a percentage of total body weight.
What is an important consideration regarding essential fat mass in genders?
Females have higher essential fat mass compared to males (12% vs 3%).
What is the significance of essential fat?
Essential fat is important for organ function.
Just like high fat mass, the loss of too much fat mass can be detrimental to health.
What factors matter in body composition measurement?
Not just the total amount or proportion, but also location and quality.
ie. visceral fat and risk of diabetes
Name the 5 techniques used to measure body composition.
- Bioelectrical impedance analysis (BIA)
- Dual X-ray absorptiometry (DXA)
- Computed Tomography (CT) + Magnetic Resonance Imaging (MRI)
- Body mass index (BMI)
- Waist circumference (WC) vs Waist-to-hip ratio (WHR)
How does bioelectrical impedance analysis (BIA) work?
Different tissues have different impedance to electrical current; more water in the tissue means less resistance.
Fat = less water.
Muscle & “other” = more water.
What are the benefits of BIA?
Inexpensive, safe, portable, easy to use.
2 or 3 compartment model
List the weaknesses of BIA.
- Low accuracy/validity - Typically underestimates body fat percentage
- Can be affected by hydration status, temperature, limbs touching, and body fat location.
How does Dual X-ray absorptiometry (DXA) work?
Two sources of low dose X-ray radiation pass through the body.
What are the outputs of DXA?
Fat mass (FM), fat-free mass (FFM), and bone mass (BM).
As well as total and regional FM
What is the ‘gold standard’ for measuring bone mineral content?
Dual X-ray absorptiometry (DXA).
List the additional benefits of DXA
Non-invasive, quick, highly reliable/ valid, 3 compartment model.
What is a significant weakness of DXA?
Cannot measure intra-abdominal fat.
Also expensive, large equipment, not portable, requires trained technician…
How does computed tomography (CT) work?
Uses a rotating X-ray to create a 3D image of internal structures.
Anatomical approach
What are the benefits of CT?
Highly reliable/valid, important for disease management, provides a 4 compartment model.
4 compartment model: Separate fat (visceral vs subcutaneous), bone, muscle mass, and other.
What is a significant weakness of CT?
High dose radiation exposure, making it unsuitable for all populations.
Also expensive, large, requires a trained technician.
How does magnetic resonance imaging (MRI) work?
Uses a big rotating magnet to create a 3D image of internal structures.
What are some key benefits of MRI?
- No radiation exposure
- Highly reliable/ valid
- Important for disease management (e.g., cancer)
- 4 compartment model: Separate fat (visceral vs subcutaneous), bone, muscle mass, and other
What are the weaknesses of MRI?
Expensive, large, requires a trained technician, claustrophobia.