Body Composition Flashcards

Question

What are the limitations of BMI

Answer 1

BMI lacks accuracy when estimating % fat of individuals Does not consider the quality of weight (i.e.) fat vs lean BMI of 25 or 30 does not correspond to the same % fat at different ages Ethnic group differences

Answer 2

Location (as well as the amount) of fat is important to health People who gain weight in the abdominal area = “apples” ↑ disease risk People who gain weight in the hip area= “pears”

Answer 3

Predicts disease risk according to “apple” or “pear” shape Waist circumference → level of the umbilicus Hip circumference → largest circumference around the buttocks

Answer 4

Based on the principle that approximately half of the body’s fatty tissue is directly beneath skin Reliable measurements of this tissue give an indication of percent body fat Measurement: Pressure calipers Right hand side of body Typically 4 sites (summed) % fat is estimated from total mm

Answer 5

Resistance to the flow of an electrical current through the body is related to total body water (72.5% FFM) (i.e.) fatty tissue is a less-efficient conductor of an electrical current Sensor electrodes are applied to the skin and a weak (non detectable) electrical current is transmitted through the body Resistance to the flow of the current is measured and used to estimate body fat, lean body mass, and body water Accuracy is similar to skinfolds, but affected by hydration state

Answer 6

Based on the 2-compartment model of body composition (i.e.) body weight is the sum of FAT and FAT FREE MASS Assumed that the density of each compartment is known and constant Typically: Density of fat = 0.9 kg/l Density of fat-free mass = 1.1 kg/l (Siri, 1956) Body Density = mass of the body/body volume % Fat = 4.95 – 4.5 x 100 where d = body density d

Answer 7

One of the oldest methods of measuring body composition Almost all other indirect techniques have been validated against hydrostatic weighing ▪ Known as underwater weighing ▪ The weight of the subject is first measured in air and then while totally immersed in water from which body volume is calculated Correction made for volume of air in: ▪lungs (either directly measured or prediction equations) and ▪Gut (standard 100ml is assumed for gut volume)

Answer 8

Time consuming Not feasible to test a large number of people Requires measurement of lung and gut volume (if unknown, can be estimated) Difficult to perform on the aquaphobic

Answer 9

Individual sits inside small chamber Computerized pressure sensors determine the amount of air displaced by the person Body volume is calculated by subtracting the air volume with the person inside the chamber from the volume of the empty chamber (air in the lungs is taken into consideration) Body density and percent body fat are then calculated Less cumbersome to administer Takes only about 5 minutes

Answer 10

Dual energy X-ray absorptiometry (DEXA) ◦Magnetic resonance imaging (MRI) ◦Computed tomography (CT) ◦Total body electrical conductivity (TOBEC)

Answer 11

Frequently used by research and medical facilities Considered by many as the gold standard technique for body composition assessment Uses low-dose beams of X-ray energy Measures fat mass, fat distribution pattern, and bone density Procedure is simple; takes only 15 minutes to administer

Answer 12

There is no “best” method for measuring body composition in living subjects Every method has errors Some methods require expensive laboratory equipment (e.g.) DXA and could not be used in community studies