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Q.
Can
you compare a handheld body fat
calculator (that sends a weak electrical
current through your body to calculate
body fat percentage) to a person's
Body Mass Index? Are the two comparable
at all? If
a person's body fat percentage is
calculated with the hand held device
(I believe it is called bio-impedance)
and then their BMI is calculated
using the formula, would you expect
the two numbers to agree? If so,
what are the similarities? And if
not, what is the difference?
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Your bodyfat percentage and Body Mass Index
are actually two very different numbers that
can have very little to do with each other depending
on several factors.
Your
body fat percentage (regardless of the source
you get it from, be it the handheld bio-impedence
electrical machine or through skinfold calipers)
is a measure of how much fat you have on your
body compared to lean mass in form of muscle,
bone, organs, etc. For example, if you weigh
200 pounds at 10% bodyfat, you are carrying
20 pounds of fat on you.
Your
Body Mass Index is a measure of weight compared
to height. It actually has nothing to do with
fat or muscle or anything like that!
Using
our same example, a person who weighed 200 pounds
at 10% bodyfat could be categorized as obese
unless they were at least 6 foot 4!
Body
Mass Index is a simple, quick gauge of your
body based on the combined average data of the
measurements of millions of people. It does
not necessarily apply to an individual. Your
bodyfat percentage is a far more useful number.
I
would expect these two numbers to agree only
if the person being tested were completely average,
which is hard to expect in the real world.
As
an aside, the bio-impedence method of testing
bodyfat may be convenient but it is not all
that accurate. The readings can vary greatly
during the course of a day and can be affected
by how much water you have in you as well as
what you've eaten during the day.
For
best results, use it at the same time every
day (preferable first thing in the morning before
doing anything else). This will give you a standardized
way to compare your results.
Personally,
those standing bodyfat scales are pretty much
a waste of money. I actually have one (Tanita
Ironman scale that's supposedly tuned for athletes)
and it pegs me at anywhere between 20% to 36%
bodyfat even though I'm about 8 to 10% or so.
What
IS interesting to think of is that the scales
you stand on are really only measure bodyfat
in your LOWER body. The current goes from one
foot to the other the quickest route possible.
They may have formulas to estimate upper body
fat and get a total but this fact makes it very
innaccurate for total body testing. For best
results, you need to go from right or left hand
to opposing foot to get a cross-section of the
whole body.
As
for hyrdation, the better hydrated you are,
the lower your bodyfat levels will record. Water
is a good conductor and more of it means the
current goes through easier (and muscle has
more water than fat). Also, if you're hydrated,
you'll weigh more than if you are dehydrated,
which will result in lower readings.
Same
goes for eating salami (or any sodium-rich processed
foods). The sodium conducts the current well
and gives lower readings.
These
bf scales are good as a curiosity but I wouldn't
put any stock in them in terms of giving legitimate
numbers, to be honest.
The
one I have cost me $120 and is a supposedly
good quality BF scale and it still doesn't work
well for me. If you get a cheap one, you'll
really be guessing. You're better off with a
regular scale and tape measure to throw around
your waist in terms of feedback on fat loss.
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