By Martica Heaner, M.A., M.Ed., for MSN Health &
Fitness
Q. According to
the BMI chart, Im officially overweight with a score of 27. But
Im only 200 pounds at 6 feet tall. I run five times a week, do
calisthenics three times a week and feel great. I would need to
drop 15 more pounds just to be considered normal weight. Is there
something off about this system?
A. Scientists
need ways to measure what they study in order to make objective
comparisons. The Body Mass Index is a tool to estimate how fat a
person is. A person with a BMI of 25 or above is considered
overweight; a BMI of 30 and above is considered obese.
The average person tends to jump on a scale and use their weight as
a gauge of their fatness. BMI tends to be more precise than just
considering body weight alone because a persons height makes a
difference. Being 185 pounds, for example doesnt say much unless
you know more about the persons shape. A person who is 5-foot-3
and 185 pounds, for example, is overweight and probably has health
risks associated with their extra body fat. But a person who is
6-foot-3 and 185 may be underweight and therefore be less prone to
obesity-related health problems.
The best way to gauge a persons level of fatness is to measure it
directly, such as when using lab equipment such as underwater
scales, dual-energy X-ray absorptiometry (DXA) and other methods.
But these methods require pricey equipment and experienced lab
technicians. Plus, some studies are so large, involving thousands
of subjects, that its not practical to obtain this
information.
So researchers who have studied obesity or the health risks
associated with being fat often use the BMI as an indicator of
excess body fat because its convenient and gives a better picture
than just taking body weight alone.
Because the only data that is needed to determine a persons BMI is
their height and weight, and this can be measured directlyor even
relayed verbally by a study participant in a telephone
interviewits a measure thats often used, especially in
large-scale, epidemiological studies. Links can easily be made
between the BMI and eating habits or health risks of, say, 50,000
people who are surveyed.
The BMI works well for research purposes, but doesnt necessarily
translate precisely to the individual. Unfortunately, it tends to
convey that people that exercise regularly, for example, are
overweight, when they are not actually overfat. A fit person tends
to have more muscle, so their body weight is a reflection of body
fat as well as muscle and other lean tissue.
Since the problem with being overfat is that health risks are
increased, a BMI in the overweight range is probably not a negative
indicator for a fit person. Regular exercise, low body fat and
increased muscle mass are all factors that tend to outweigh any
health risks suggested by a higher BMI.
In other words, if you know you are fit, not fat, you dont need to
worry about your BMI. But the Centers for Disease Control (website)
points out that those with a BMI in the obese range (higher than
30) do tend to be overfat, even if they are fit. So, this may
increase disease riskalthough research does show that being fit
and fat is still healthier than being thin and unfit.
