| Method |
BMI (Body Mass Index) |
Hydrodensitometry
(Underwater Weighing) |
Anthropometry (Skinfold
Measurements) |
Near-Infrared
Interactance |
Dual Energy X-Ray
Absorption (DEXA) |
BIA
(Bioelectrical Impedance Analysis)
| Tanita BIA (Leg-to-Leg)
|
| Procedure |
Weight and height are
measured then BMI is computed using a simple formula or chart. |
Subject is weighed
then immersed in a tank of water while fully exhaling.
Measurements of immersed weight
are repeated as many as 5 times and then averaged. |
Skinfold thickness is
measured by grasping the skin and underlying tissue, shaking it to exclude
any muscle and pinching it with a caliper.
Measurements are taken at 1, 3,
5, 7 or 21 locations and entered into a formula. Multiple readings
at multiple sites improve accuracy. |
A fiber-optic probe
connected to a digital analyzer indirectly measures tissue types at
various body sizes to a depth of about 1 cm.
NIR data is combined with height,
weight, frame size, and athletic level to estimate percent body fat.
Multiple readings at multiple sites improve accuracy. |
Based on a
three-compartment model that divides the body into total body mineral,
fat-free soft (lean) mass and fat tissue mass.
A whole body scanner reads bone
and soft tissue mass simultaneously. Scanner passes over reclining
subject once collecting data at .5 cm intervals. |
With
traditional BIA a person lies down and spot electrodes (with electrolyte
gel) are placed on a hard and bare foot. The resistance of a small
electrical signal is measured as it passes through the body.
This measurement is
entered into a formula along with height, weight and gender to determine
lean and fat mass.
| Weight and impedance
are measured in a single step while subject stands barefoot on the device.
Measurements are combined with subject's
gender, height and age (which are programmed into the device) to
determine body fat based on multi-ethnic, diverse population formulas that
have been highly researched and validated. |
| Test Time |
1-2 minutes |
15-60 minutes |
10-20 minutes |
Under 5 minutes |
10-20 minutes |
5 to 10 minutes |
30 seconds |
| Subject Comfort |
No discomfort. |
Difficult for subjects
who dislike submersion or have difficulty expelling all the air in their
lungs. |
Subject must be
"pinched" at exposed areas on various parts of their body. |
Low discomfort,
primarily with single site method. |
Safe and non-invasive,
requiring only that a subject must lie still throughout the procedure. |
Electrolyte gel can be
uncomfortable. Subject must lie down for procedure. |
No discomfort. |
| Technician Skill |
Low |
High |
High |
Moderate |
High |
Moderate to low |
Low |
| Subject Cost |
Very low |
High |
Low |
Low to moderate |
High |
Low |
Low |
| Equipment Cost |
Very low |
Very high |
Low to moderate |
Moderate to high |
Very high |
Moderate to high |
Low to high |
| Acceptance |
Used in clinical
settings as simple indicator of obesity.
National Institutes of Health and
World Health Organization have developed basic BMI screening guidelines. |
The traditional
reference method for body composition research. |
Widely used due to low
cost of equipment and portability.
Over 3,500 equations have been
validated to account for differences in gender, age, and ethnic groups.
To save time single readings are
often taken providing only a rough estimate of body fat. |
Popular outside the
laboratory because it is simple, fast, non-invasive and relatively
inexpensive.
While single-site measurement at
the biceps is often used, numerous sources report that more research is
needed to substantiate the validity, accuracy and applicability of this
method. |
Quickly moving the
laboratory setting into clinical studies.
Measures fat distribution
throughout the entire body in a single scan.
Originally used to measure bone
density. |
Long-accepted because
of simplicity, low cost, high reproducibility and non-invasiveness.
New BIA techniques (phase angle
and multi-frequency) are under development for estimating hydration and
intra/extra-cellular breakdown. Additional research is needed to
refine those method's accuracy in determining body fat percentage. |
Offers advantages of
traditional BIA as well as greater ease of use, speed and portability.
Quickly being accepted in
professional settings including hospitals, labs, health clubs, weight loss
clinics and doctors offices. |
| Reliability and
Reproducibility |
Current guidelines do
not differentiate for gender, ethnicity, or age.
Can be misleading for
non-standard body size and shapes, athletes who are overweight but have
low body fat, and for sedentary individuals who may have normal BMI but
high body fat. |
Readings may vary due
to changes in hydration and proportion of bone minerals.
Requires multiple readings that
are then averaged.
If remaining air in lungs is
estimated, errors can occur. |
Precision depends
heavily on the skill of the technician.
Accuracy is also affected by
which sites are measured, the number of sites measured, the taking of
duplicate readings, the quality of calipers, and the equation used.
Calipers developed for home use
(very inexpensive) are unreliable.
The more obese a subject, the
more difficult it is to grasp the skinfold correctly. |
High degree of error
has occurred with very lean and obese people.
Amount of pressure applied to
fiber optic probe, skin color and hydration levels may be sources of
error. Low number of readings can increase error.
Sold by only one manufacturer.
Technician determines fitness
level (body type) as in other methods.
Measurements should be taken
under constant and controlled conditions to minimize variations. |
More reliable than
other measurements due to three compartment model, no need to account for
air mass in lungs, and accounts for variations in the distribution of body
fat.
High reliability and measures fat
distribution with just one measurement. |
Very high
reproducibility and accuracy given proper electrode placement.
Measurements should be taken
under constant and controlled conditions to minimize variations caused by
hydration level.
Accuracy is heavily dependent on
type of equation used. Most BIA research continues to use underwater
weighing as reference. |
Very
high reproducibility not dependent on technician training,
Equations
and equipment validated by
peer-reviewed research.
As with all
measurements, analysis should be done under consistent conditions.
Uses DEXA as
reference method for
higher accuracy. |
