Body Fat Percentage
What is body fat percentage, how do you measure it and what is a healthy range?
The amount of body fat you carry, your body fat percentage, makes a difference to your body shape and your health.
Your shape is affected by body fat percentage because muscle tissue is more compact than fat - a balloon containing 1lb of muscle tissue would be smaller than a balloon containing 1lb of fat!
So a woman, 5' 6" tall weighing 140lbs (10 stone) who does regular muscle enhancing exercise, will have a lower body fat percentage, and 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. Bioelectrical Impedance technology means that body fat monitors are now easy to operate and available for home use.
A very low level electrical signal is sent through the body - normally by standing on sensors on a body fat monitor. 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.
Tanita offer a range of body fat monitors / scales for use at home - click here for details.
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 inaccurate.
Hydrostatic Weighing Tanks
This method is the most accurate 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 make sure no air is trapped in your lungs, otherwise the test will be inaccurate and your results will make you appear fatter.
This technique involves a different coloured light, which is shone onto the skin surface at selected areas. The spectrum of the wavelengths reflected is analysed by computer. The lean : fat ratio at the test areas can be calculated as fat and lean tissue have different interactive spectra.
This method is not recommended because researchers have found prediction errors.
How much body fat is healthy?