Week 3: Body Composition Flashcards
Body Composition
-Body composition refers to the components that make up the body
-Body weight and relative amounts of muscle, fat, bone and other vital tissues
-Often limited to fat and lean body mass (fat-free mass) and expressed as
relative (percentage) and absolute (kilograms)
-Body composition is frequently used as an outcome measure to determine the
effectiveness of community-based obesity prevention strategies.
-Currently, universally accepted norms for body composition do not exist
-A consensus opinion for an exact percent body fat value associated with optimal
health risk has yet to be defined, but there is a range
Skinfold percentile reference values the “good” category
-12%– 23% for males
-17%–26% for females
Why do we measure body composition?
- Risk of metabolic diseases
-Obesity is related to health risks, including:
⁃ Cardiovascular disease
⁃ Peripheral vascular disease
⁃ Hypertension
⁃ Type II diabetes
⁃ Metabolic syndrome
⁃ Sleep disorders
⁃ Stroke - Maximize performance/health
- Research outcome
Body Composition Models (2)
-Two-component models
-Three-component models
Two-component models (6)
- Anthropometry (circumference measures)
- Skinfold thickness
- Bioelectrical impedance analysis
- Underwater weighing
- Plethysmography (Bod Pod)
- Ultrasound
Three-component models (3)
- Dual-energy x-ray absorptiometry (DEXA, DXA)
- Magnetic resonance imaging (MRI)
- Computed tomography (CT)
Body Composition Techniques
-A body composition technique is considered valid if it measures what it says it
measures (relative body fat)
-A body composition technique is considered reliable if the results are reproducible
Examples:
-weighing someone on a scale would be considered a simple, reliable measure, but in reference to relative body fat, it is not valid
-Underwater weighing (hydrodensitometry) estimates body fat and is one of the most valid measurements we have, but compared to body weight measurements, it is not as reliable.
Dual-energy x-ray absorptiometry (DEXA, DXA)
-Considered the gold-standard
-A 3-component model which provides an estimate of bone, fat, and lean tissue densities
-Expensive equipment that is usually found in research and clinical settings, high performance settings
-Full-body x-ray is used to evaluate various tissue densities
-Limitations: can’t do it with people over 6’4 and 350lbs
*3 component model
Underwater weighing (UWW)
-Also called hydrostatic weighing or hydrodensitometry
-Considered one of the most valid methods of estimating relative body fat
-Densitometry – fat and lean tissues have different densities
-Water density 1 g ml-1
-Fat density < 1 g ml-1 or approx. 0.9 g ml-1
-Lean tissue density = 1.1 g ml-1
-2-component model
-Limitations: have to blow air out of lungs and then submerge
*2 component model
Air-Displacement Plethysmography (BOD POD)
-Commercial name: BOD POD
-Densitometry technique
-Displacement of air in a sealed compartment
*2 component model
Anthropometric Assessments- BMI
-indirect measure for body fat
-Simple and reliable measure commonly used in clinical situations and
epidemiological research
-Used to classify underweight, normal, overweight and obesity classes in adults
and children
-BMI = Wt (kg) / Ht2 (m2)
Underweight= <18.5
Normal= 18.5-24.9
Overweight= 25-29.9
Class I Obesity= 30-34.9
Class II Obesity= 35-39.9
Class III Obesity= >40
Strengths:
-Simple, inexpensive, reliable measure
-National and international standards are available
-High specificity for detecting excessive adiposity with higher BMI values in adults
Weaknesses:
-Does not provide direct body fat measure
-Poor estimates of body fat in some ethnic groups, ages, body build/frame size
The American Medical Association (AMA) recognizes that BMI is an “imperfect
way to measure body fat in multiple groups given that it does not account for
differences across race/ethnic groups, sexes, genders, and age-span.”
Anthropometric Assessments- WC
Indirect/proxy method for intra-abdominal fat
Method
-The WHO STEPwise Approach to Surveillance (STEPS) protocol for measuring waist circumference:
-Measurement at the approximate midpoint between the lower margin of the last palpable rib and the top of the iliac crest
-Tape should be snug around the body and parallel to the floor
-Participants should stand with arms at the sides; feet positioned close
together, weight evenly distributed
-Measure at the end of normal respiration
-Relaxed position
Strengths:
-WC is closely linked to increased risk for chronic disease in both adults and
children
-May provide a better indicator of chronic disease risk than BMI, especially in individuals with normal BMI values
Weaknesses:
-Does not directly measure intra-abdominal fat
-Practitioner must be trained
-2-3 measures need to be taken and averaged
Very low risk= <80cm or 31.5in (men), <70cm or 27.5in (women)
Very high risk= >120cm or 47in (men), or >110cm or 43.5in (women)
*risk of CVD, diabetes, hypertension = >102 cm (men) and >88cm (women)
Field-based Body Composition Assessment Methods (2)
- Skinfold Thickness (skinfold calipers)
- Bioelectrical Impedance Analysis
Skinfold Thickness (skinfold calipers)
-Estimation of body fat
-Most widely used field technique
-Rationale = age-dependent proportion of body fat is deposited subcutaneously
-The amount of adipose tissue that can be pinched provides some indication of the amount of overall body fat
-Estimation of percent body fat from skinfold measures has an error of approx. 3.5%
Method:
-Using skinfold calipers, all measurements are taken on the right side of the body
-Carefully landmark and measure skinfold sites
-Generalized body density formulas using 3-7 measurement sites
-Body composition is estimated from the Siri equation: %body fat = (4.95 / density) – 4.50
Strengths:
-Relatively easy measurement with minimal equipment
-The relationship between subcutaneous fat and total body fat varies with race,
age and sex. Therefore, population-specific equations have been developed.
Weaknesses:
-Calipers vary in quality, and some can be grossly inaccurate
-Intra and inter-rater reliability
-Not recommended for people with BMI > 30kg/m2
Factors that may contribute to measurement error:
-poor anatomical landmark identification
-poor measurement technique
-inexperienced evaluator
-extremely obese or extremely lean participant
-improperly calibrated caliper
Bioelectrical Impedance Analysis
-Estimates fat-free mass and total body water
-Based on the body’s ability to conduct a mild electrical current to indirectly estimate fat-free mass or % body fat
-Impedance: opposition to the flow of current where electrolytes in body water conduct electrical current
-Measured with BIA analyzer
-Greater total body water current passes more easily through the body
-Fat tissue has lower water content than fat-free mass-> Impedance is greater in individuals with more body fat
-SEE = 2.7 to 6.3%
Strengths:
-Validated equation available for adults and children
-Standard error estimates available for BIA published equation
Weaknesses:
-Equations less valid for identifying adiposity in individuals with high or low BMI values
-Accuracy depends on following standardized procedures (normal hydration, fasting, and avoiding exercise
Weight Stigma
Pervasive misconceptions and stereotypes associated with higher body weight, is both a social determinant of health and a human rights issue. It is imperative to consider how much weight stigma may be impeding health promotion efforts on a global scale (Nutter et al. 2023)
“If we are concerned about health and well-being, then we need to go beyond body standards or ideals. We need to consider how healthy bodies are based on what’s going on inside rather than focusing on externalities”.
Circumference Measurements Steps
-Explain the assessment to your peer client and receive informed consent
-The client is positioned in standing for all measurements
-The tape should be placed on the skin surface whenever possible (except for the hip measurement). If taking measurements on the skin surface is not culturally acceptable or if the client is not comfortable with this, taking measurements over clothing is possible. Clothing will introduce some error to the measurements, but if taken this way,
the client should be asked to wear the same clothing at re-assessments.
-For all circumference measures measure on the right side of the client’s body
-Correctly landmark each site; you may consider using a light pen mark to improve your accuracy when remeasuring each site.
-The inferior (lower) edge of the tape should be in line with the landmark
-Ensure the tape is level/straight around the entire girth. Make sure to pull the tape straight without compression of the subcutaneous adipose tissue.
-Conduct the measurement from a position such that you are at eye level with each circumference
-Measurements are recorded to the nearest 1mm
-Take two measurements at each site and retest if duplicate measurements are not within 5mm of each other
-Rotate through measurement sites to allow time for skin to regain normal texture.
Skinfold Measures
-Explain the assessment to your peer client and receive informed consent
-Complete one round of all skinfold measurements before repeating the procedure to obtain a second measure. Two measures of each site will be obtained (or three if necessary)
-All measurements are taken on the right side of the body.
-Ensure participant is relaxed when taking measurements
- A fold of skin plus the underlying fat is grasped between your thumb and index finger with the back of your hand facing you. The fingers are placed on the skin
~ 8 cm apart and then drawn together to form a fold. This fold is pinched 1 cm above the landmark.
-Keep the jaws of the calipers at right angles (perpendicular) to skinfold.
-The jaws of the caliper are placed halfway between the peak of the fold and the base.
-While holding the skinfold, fully release the caliper trigger, and take the measurement within 4 seconds of pinch (longer results in fluid displacement in tissue). NOTE: Do not let go of the skinfold while the calipers are in use. This may cause discomfort for the client.
-Record the value to the nearest 0.2 mm.
-Calculate the mean of 2 values for each measure unless the difference between the first and second measure is greater than 1 mm. If so, take a third measure of that site and take a mean of the two values that are closest in value. If the three values are equidistant; take a mean of all three
