NIH
Technology Assessment Conferences Office
of Medical Applications of Research, National Institutes of Health, Federal Building,
Room 618, 7550 Wisconsin Avenue, Bethesda,.Maryland 20892-9120, phone (301)
496-1144, fax (301) 402-0420
FOR
IMMEDIATE RELEASE:
Contact:
Bill Hall, 301-496-4819
Wednesday, December 14, 1994 Leslie Curtis, 301-496-3583
NIH PANEL EVALUATES BODY FAT ANALYZERS
A
panel of experts convened by the National Institutes of Health today recognized
the potential value of monitors frequently used to measure body fat, but they
cautioned against misinterpreting the values derived from these devices.
Machines
using bioelectrical impedance analysis (BIA) are commonly believed to measure
body fat. However, BIA actually determines the body's ability to conduct an electrical
current, which reflects the total amount of water in the body. This measurement
is then used to determine an estimate of body fat levels.
The
panel recognized the importance of BIA in assessing the body composition of healthy
individuals and of those with a number of chronic conditions. However, the panel
expressed concern about the lack of standardization of these devices, especially
in light of their wide use in health clubs, physicians' offices and hospitals.
These machines are preloaded with software
to calculate body fat based on the measurement of body water. Within each machine
there are built-in assumptions about individual characteristics with regards to
age, ethnicity, body size and fitness level.
BIA
can give estimates of body fat levels, but it's unlikely that it will measure
short-term changes in body fat or muscle as a result of increased physical activity
or changes in diet. While standardizing BIA machines may improve their accuracy,
we must also focus on improving the technology itself," said panel chairman Dr.
John Rombeau, professor of surgery at the Hospital University of Pennsylvania
in Philadelphia.
During BIA, electrodes
are placed on a wrist and ankle, and a very low electric current, which cannot
be felt, is passed through the body. The change in voltage between electrodes
measured and used to determine the person's total body water. Calculations are
then made using this information, which results in an estimate of body fat.
Before
undergoing BIA, certain requirements for testing should be met. The panel recommended
that persons being tested should be lying down at least several minutes and have
not eaten for at least 4 hours. Other factors the panel identified as affecting
the test results include recent moderate to strenuous exercise, dehydration, and
skin and room temperature. This test may prove to be less accurate in assessing
extremes in body composition.
Among their
recommendations for future research, the thirteen member panel emphasized the
need to learn more about how BIA works and the scientific principles upon which
it is based. The group also recommended that the equations used to derive body
ft estimates be made available to researchers and clinicians in an effort to allow
more uniform application of BIA. Additionally, the experts recommended further
studies to determine if population-specific equations may be needed to estimate
body fat in older people as well as in the very lean, the obese, and ethnic groups.
The panel also recommended the establishment
of a committee of scientific experts and industry manufacturers with the goal
of setting instrument standards and procedural guidelines.
These
conclusions and recommendations were issued at the end of a 2-1/2 day Technology
Assessment Conference on Bioelectrical Impedance Analysis in Body Composition
Measurement, sponsored by the National Institute of Diabetes and Digestive and
Kidney Diseases and the NIH Office of Medical Applications of Research.
A
full copy of the technology assessment statement can be obtained by contacting
the NIH Office of Medical Applications of Research at the address listed above.
