What is body fat
percentage, how do you measure it, and what’s a healthy range?
The amount of body fat you carry, or your body fat percentage,
makes a difference to your body shape and subsequently, your health.
Your shape is affected by body fat percentage because muscle tissue is more
compact than fat – a balloon containing 1 pound of muscle tissue would be
significantly smaller than a balloon containing 1 pound of fat!
For example, a woman standing 5' 6" tall and weighing 140lbs (10 stone)
who does regular strength training exercises will have a lower body fat
percentage, and therefore look slimmer, than a woman of the same height and
weight who doesn't exercise and therefore has a higher ratio of body fat.
Measuring changes in body fat percentage, rather than just measuring changes in
weight, can be very motivational when you're dieting – especially if you are
exercising as part of your weight loss regime.
How body fat is measured
Until fairly recently, measuring body fat percentage required the
help of professionals. The development of Bioelectrical Impedance technology
means that body fat monitors are now easy to operate and available for home
A very low level electrical signal is sent through the body – normally by
standing on sensors located in a body fat monitor (i.e., in a scale). The
signal travels quickly through lean tissue, which has a high percentage of
water and is therefore a good conductor of electricity, and more slowly through
fat, as fat has a lower percentage of water and is therefore a poor conductor
of electricity. Bioelectrical Impedance devices use the information from this
signal to work out body fat percentage for you.
This method involves a skinfold caliper to pinch
predetermined sites on the body. The tongs pinch the skin,
pulling the fat away from the muscles and bones. A gauge on the
calipers measures the thickness of that pinch.
It is recommended that this test is carried out by a
professional and should be repeated to verify measurements. To
make the test reliable you should not exercise beforehand.
Exercise makes your blood travel to your skin to help you cool
down and this causes the skin to swell, making your test
Hydrostatic Weighing Tanks
This method is the most accurate weigh to determine body fat
percentage, but also the most uncomfortable. You sit on a scale in a large tank
of water and blow all the air out of your lungs, then submerge yourself in the
water completely. You stay underwater for 5 seconds, while your underwater
weight is recorded. You have to ensure no air is trapped in your lungs, or the
test results will be inaccurate and your results will make you appear
This technique involves using an infrared light, which is shone
onto the skin surface at selected areas (usually the biceps). The spectrum of
the wavelengths reflected is analyzed by computer. The lean : fat ratio at the
test areas can be calculated as fat and lean tissue have different interactive
Note: This method is not highly recommended because researchers
have discovered prediction errors.
How much body fat is healthy?