Body composition - 6

why is body composition so important

• As an indicator health status

• To help favor optimal performance

• To monitor changes in body composition (growth, aging, disease)

• To evaluate efficacy of treatment (e.g., exercise, diet, drug interventions designed to change body composition)

• Excess fat is associated with many diseases

what are different ways we can measure the quantity of body comp

• Fat Free Mass (FFM) = Body weight – Fat mass

  • large part is total body water, around 50% of FFM is muscle mass, can still include some lipids

• Lean Soft Tissue (LST) = FFM - bone mineral

fats vs lipids

fats - white substance solids at room temp like triglycerides and is not a cell or tissue its a molecule

lipids - non hydro soluble molecules (constists of a lot of things)

what are different tools to assess body comp at the different levels

• Bioelectrical impedance analysis (BIA)

• Dual X-ray absorptiometry (DXA, aka DEXA)

• Computed Tomography (CT) + Magnetic Resonance Imaging (MRI)

• Body mass index (BMI)

• Waist circumference(WC) vs Waist-to-hip ratio(WHR)

• its not just about the total amount or porportion but its also the location and quality

what is BIA for body comp

• Different tissues have different impedance (resistance) to electrical current.

• Less resistance = more water

• Main issues:

  • Larger “cylinders” have less resistance (ex. legs, trunk, arms), higher diameter = less resistance

  • Water to FFM ratio - intracellular vs. extracellular

  • Hydration status, temperature

  • Position of arms and legs

• there are a qualitative analysis (phase angle eval for intra/extra cellular water ratio and Bioelectrical impedance vector) and quantitaive analysis (body comp estimation)

what is DEXA for body comp

• Often considered “gold standard” - used for bone mineral density

• FM + BM (bone mineral)+ FFST (fat free soft tissue)

• Cannot measure intra-abdominal fat - an estimate of density is estimated again to get this value and doesnt always work that well

what does a CT or MRI tell you about body comp

• the distribution of fat

• visceral fat - the black inside surrounding organs, considered more harmful metabolically

• subcutaneous fat - the white outside, fat under the skin, less harmful

• ppl can have the same total fat but the location of it can be different, which is why BMI doesnt tell the whole story

• visceral fat is an independent factor of dying, subcutaneuos fat doesnt predict death and is protective

• liposuction - removing subcut fat didnt help with health outcomes but removing visceral did

what are the functions of visceral fat

• supplies blood to the intestines with the superior mesenteric artery

• carries blood from intestines and abdominal organs to the liver with the hepatic portal vein

BMI vs WHR in predicting heart attack risk

• WHR is better at predicting it, is a stronger predictor on its own

• higher WC is a predictor and higher HC leads to reduced odds of having a heart attack (HC is inlfuenced by muscle mass)

what is WC more associated with

• Waist circumference more strongly associated with abdominal fat than WHR.

what is the limitation of WHR in defining obesity

• it might miss some changes

what is the difference in fat quality between different groups of people

• lean sedentary ppl have high insulin sensitivity and around 1-1.5% of muscle lipid

• obese ppl have less insulin sensitivity and around 2% of muscle lipid

• type 2 diabetes people have very low insulin sensitivity and around 3% of muscle lipid

• athletes have around 2.5% of muscle lipid but very high insulin sensitivity which is the athletes paradox

  • insulin sensitivity means that your body does what it tells you

why are all myocytes not the same

• muscle cells are not the same because after exercise intervention there are alot more mitochondria but the fat within the muscle doesnt change that much (became smaller sized lipid droplets)

• people with smaller lipid droplets had more insulin sensitivity

• people with more increase in mitochondria had more insulin sensitivity

why are all adipocytes not the same

• White vs. Brown vs. Beige adipose tissue - not all fat have the same risk

• Large vs. small adipocytes

  • Hypertrophy vs. hyperplasia

  • What is better for a given volume: many small adipocytes or a fewer/larger ones?

• Inflammation

what are the functions of white adipose tissue

• Energy storage

• Insulation for organs

• Protection, “packaging” - against infections

• Endocrine role, inflammation - immunity

• 90-95% of our fat cells are white

what matters with white adipose tissue

• Adipocyte size matters - there is a limit and as you get close there is more risk and develops insulin resistance

• Hyperplasia (differentiation from pre- adipocytes)

• Hypertrophy (increase in volume)

apoptosis vs necrosis

• Apoptosis: controlled and mostly non- inflammatory cell death, normal

• Necrosis: cell death involving macrophage recruitment and inflammatory responses, not normal (from stress or size)

facts and functions about brown adipose tissue

• Originally believed to only be in other mammals (e.g., hibernating) or human infants.

• Production of body heat without shivering

• Brown color due to presence of more capillaries and mitochondria

• Numerous/smaller lipid droplets vs. white adipocytes

• Now confirmed in humans, but lower amounts with aging, obesity or absence of cold exposure

• Can be subcutaneous (e.g., near clavicles, between scapula...) or visceral (e.g., around blood vessels, and organs such as kidneys) - to produce heat

what type of adipose tissue is the intermediate between brown and white

• beige adipose tissue

• Brown adipocytes come from same stem cells as muscle

• “Beige” or “brown-like” adipocytes - help ppl generate heat, exercise miht help regulate them

• White adipose tissue contains darker adipocytes that come from same precursors as WAT (e.g., near clavicle or spine)

what is a summary of body composition

• Many important tools for estimating body composition.

• Need to consider absolute amount, relative amount, location, and “quality”.

• Do not be obsessed by numbers or “cutoff”

  • Body composition is but one factor to estimate “risk” or “performance”

• subcut fat is the healthier way to store fat

check practice questions posted