CEC
ARTICLE
Title: Comparison of multi-frequency bio-electrical impedance and DXA
on body composition
Authors: Dr’s Wang and colleagues. (School of Public Health, Bejing,
China)
Source: Biomedical and Environmental Sciences (2018) 31(1): 72-75. Click
HERE to read.
Introduction: As an Accredited Exercise Physiologist (AEP), the
clear majority of my patients see me for the purpose of undertaking
rehabilitative exercise. Unfortunately, there is still not a big interest in
preventative exercise prescriptions from AEPs. That being said, as I
am located in a medical centre I receive the majority of referrals from
general practitioners and specialists, as the patients typically have
chronic diseases and conditions. On the bright side, the apparently
healthy individuals are being cared for by personal trainers and
group fitness instructors.
We recently had an interesting case which we will present as
a case study here. Alan (not his real name) is a middle-aged male
with a family history that includes type 2 diabetes mellitus (T2dm,
mother, father and both brothers), coronary heart disease (father
and mother and paternal and maternal grandparents), hypertension
(mother, father and brothers) and dyslipidemia (mother, father and
brothers). Alan’s medical history includes obesity (BMI 34.1kg/
m 2 ), hypertension (resting blood pressure was 146/88mmHg when
we tested), dyslipidemia (total cholesterol 6.1mmol, high density
lipoprotein 0.9mmol, low density lipoprotein 3.7mmol) and HbA1c (a
test for type 2 diabetes mellitus) reading of 6.3%, which classifies
as prediabetes. His prescribed medications include Betaloc (anti-
hypertensive) and Lipitor (for cholesterol) to which he is compliant.
Alan’s general practitioner referred him to our clinic, citing the
reasons for doing so as being to ‘reduce his likelihood of developing
T2dm, weight management, blood pressure control and improved
lipids’. These referrals are usually very short and to the point.
Alan is employed as an accountant (full time), presented with no
musculoskeletal injuries (or history of musculoskeletal injuries) and
his current physical activity consists only of incidental walking,
specifically to and from his car and moving around his house. We
devised an individualised exercise prescription for Alan and he went
off to his local gym to embark upon it. Upon follow-up two weeks
later, Alan presented his workouts, which he was tolerating well,
along with a body fat test that had been conducted using a bio-
electrical impedance analyser (BIA). In brief, the results showed his
body fat to be an athletic 18%! No way in h*ll – so we referred Alan
for a DXA scan to see if that would tell a different story… DXA stands
for dual-energy X-ray absorptiometry, a process of conducting a full
body scan for segmental body composition. This scan found Alan’s
body fat to be much higher, at 37.1%. This leads us into this Research
Review, in which we look at Dr Wang and his colleagues’ comparison
of the accuracy of a bio-electrical impedance analyser (BIA) to that
of a DXA scan.
BIA’s have been around since the mid 1980’s, and admittedly
there is a wide range of units available designed for everything from
home use to application in the clinical/medical setting. One would
therefore expect differing degrees of accuracy between these units.
BIA machines have lower accuracy compared to units using four (one
per hand and foot) or more electrodes, and
poorly insulated wires have been shown to
be sensitive to room temperature, thereby
affecting the results.
DXA, on the other hand, is considered to
be the gold standard (i.e. the diagnostic test
that is considered to be the most accurate)
for determining body composition and is
especially beneficial as it provides segmental
results for lean mass (muscle) and fat mass
(adipose). In DXA scans, two different energy
levels of X-ray pass through the body and
measure fat, muscle and bone levels. It also
provides specific details about where the fat
and muscle are situated on the body.
The authors compared a BIA to DXA in
determining body composition in a large
cohort (749, males and females) of obese
adults. All participants were required to have
a body mass index (BMI) > 28kg/m 2 and be
aged 25-55 years of age. Participants had
both BIA and DXA measurements taken
following an 8-hour (or more) fast and
according to manufacturers’ requirements.
Results: The per cent body fat estimated
by the BIA was significantly lower (-4.33%)
as compared to the DXA scanner in the
males and significantly higher (+0.5%) in
the females, which was a real problem.
Given these findings, the researchers then
created correction equations to improve the
accuracy of the BIA device.
The authors concluded that body
composition is widely used in clinics, weight
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