APK 3110C Lecture Notes - Lecture 13: Body Fat Percentage, Dual-Energy X-Ray Absorptiometry, Rheumatoid Arthritis
6 May 2018
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APK 3110
Body Composition, Obesity, Weight Control
BMI
• Body Mass Index
o BMI = body mass (kg)/ Height (m^2)
• As BMI increases above normal ranges so does risk for cardiovascular complications,
cancer, diabetes, Alzheimer’s disease, gall stones, sleep apnea, osteoarthritis, rheumatoid
arthritis, renal disease
Limitations of BMI
• Body composition
o Does not separate lean mass from fat mass
o Athletes
▪ Higher muscle mass
▪ Increase plasma volume
▪ Heavier bones
Fat Stores
• Essential fat
o Fat in heart, lungs, liver, spleen, kidney, intestines, muscles, CNS tissues, bone
marrow
o Required for normal functioning
▪ Women about 10-12 percent of body mass
• This is because of reproductive needs
▪ Men about 3 percent body mass
• Minimum fat
• Storage fat
o Similar percentage in men and women
o Mostly that in the adipose tissue
o Visceral fat that protects organs in thoracic and abdominal cavity
o Subcutaneous fat under skin
o About 19 pounds in reference man = 63500 kcal of stored energy
o (fat that makes you look fat)
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Models for Assessing Body Composition
• 2 compartment models
o fat and fat-free mass
▪ FFM = Bone, water, muscle connective tissue, organ tissue, and teeth
• 4 compartment models
o water, protein, minerals (bone) and fat
o Used in DEXA and CT
Assessment of Body Composition
• Direct
o Chemical analysis of animal carcass or human cadaver
• Indirect
o Estimation using laboratory technique
▪ Hydrostatic weighing
▪ Skinfolds/ girth measurements
▪ Computed tomography, MRI, DEXA
Hydrostatic Weighing – Underwater Weighing
• Density = mass/volume
• Body volume = body mass in air – body weight under water
o Must correct for temperature when calculating density of water
o Weigh person in air/on land first
o Weight of apparatus is subtracted from body weight under water
• If you don't exhale at maximum then you will have a increase in fat mass
• Gold standard
Limitations of Hydrostatic Weighing
• Constants used in the equation for fat free and fat tissue compartment assumes that these
are the same across all people
o African Americans and Hispanics have high average density of FFM than whites
o During growth (children) osteoporosis the water and mineral content of FFM Is
changing
▪ Reduced bone density means density of FFM is reduced and body fat is
overestimated
o Male weightlifters have a lower FFM density due to larger water and smaller
protein and mineral fractions which means overestimated percentage body fat
Bod Pod
• Measures body volume by measuring the volume of the empty chamber compared with
the volume of it with the person inside of it
o Pulmonary gas volume is measured and subtracted from body volume
• Body density = body mass in air/ body volume in bod pod
• More commonly used
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