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.
What is the body mass index (BMI)?
A weight to height ratio expressed in kg/m2.
Index of relative weight
What are the benefits of BMI?
Fast, easy to measure, low cost, minimal participant involvement, and correlated to many health outcomes.
Screening/ tracking tool.
What is a significant limitation of BMI?
Does not provide information about location or quality of weight.
Also not appropriate for some populations.
What does waist circumference (WC) measure?
Circumference of the waist, expressed in cm.
What are the benefits of measuring waist circumference?
Fast, easy to measure, low cost, and abdominal region specificity.
Screening/ tracking tool.
What is the limitation of measuring waist circumference?
Individual vs. population level indicators.
What is the waist-to-hip ratio (WHR)?
A ratio comparing waist circumference to hip circumference.
No units.
What are the pros and cons of measuring waist to hip ratio (WHR)?
Pros: Fast, easy to measure, low cost, minimal participant
involvement. Screening/tracking tool.
Cons: N/a
What is a key finding regarding BMI, WC, and WHR related to myocardial infarction (MI)?
As WHR and WC increase, the risk of MI increases; controlling for BMI shows no increased risk.
How do changes in BMI affect the odds ratio (OR) of having MI?
As BMI increases, OR of having myocardial infarction increases.
Controlling for waist to hip ratio (WHR) shows no increased risk.
What is the difference between intramuscular lipids and other fat?
Intramuscular lipids are located within skeletal muscle fibers and are associated with T2D risk.
What is the relationship between intramuscular lipids and T2D?
Increased intramuscular lipids are associated with a decrease in insulin stimulated glucose disposal (i.e., increased insulin resistance).
What are myocytes?
Muscle cells
What occured with a 4 month calorie restriction and PA in the previously sedentary?
Decrease in BW by 10%
Increase in VO2 max
Increase in insulin sensitivity
Increase in mitochondria
Decrease in lipid size
No change in IML (%)
What are the positive relationships in body composition?
- Regular exercise and mitochondrial oxidative capacity
- Regular exercise and intramyocellular lipid
- Obesity and intramyocellular lipid
- Mitochondrial oxidative capacity and insulin sensitivity
What are the negative relationships in body composition?
- Obesity and Mitochondrial oxidative capacity
- Insulin sensitivity and ceramide & diacylglycerol
What are the three types of adipose tissue?
- White adipose tissue (WAT)
- Brown adipose tissue (BAT)
- Beige adipose tissue.
What is the relationship between lipid droplet size, mitochondria size, and insulin sensitivity?
Insulin sensitivity increases as a result of…
Lipid droplet size decreasing and mitochondria size increasing.
What is the main role of white adipose tissue (WAT)?
Energy storage, protection, insulation, and an endocrine role.
What is the function of brown adipose tissue (BAT)?
Production of body heat without shivering.
What are the characteristics of brown adipose tissue?
Brown color due to presence of more capillaries and mitochondria.
Numerous/smaller lipid droplets vs. white adipocytes.
Now confirmed in adult humans, but lower amounts with aging, obesity, or absence of cold exposure.
Subcutaneous (e.g., near clavicles, between scapula…) or visceral (e.g., around blood vessels, and organs such as kidneys)
How do beige adipocytes differ from white adipocytes?
Beige adipocytes can produce heat and come from the same stem cells as muscle.
What is the significance of adipocyte size?
Adipocyte size affects hyperplasia and hypertrophy, influencing health outcomes.
Hyperplasia: enlargement of an organ.
What is the relationship between obesity and hyperplasia?
As obesity increases in
severity, hyperplasia
becomes most evident.
What are the two types of cell death in adipose tissue?
Apoptosis: controlled, mostly non-inflammatory
Necrosis: inflammatory response and macrophage recruitment.
What is the relationship between the amount of macrophages and subcutaneous vs. visceral obesity?
More macrophages in individuals with visceral obesity, leading to more inflammation - insulin resistance, T2D, etc.
What is the conclusion about body composition measurement?
Consider absolute amount, relative amount, location, and quality without obsession over numbers or cutoffs.
