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Ways to Measure Body Fat
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What methods are available to measure body fat and how accurate are they?

Disclaimer:

It should be made clear that there is only one method of calculating body composition that is close to 100% accurate, and that is an autopsy. Since none of us are planning on that right now, realize that ALL of the methods listed below are relative accuracy measurements, not absolutes!!!!!

Hydrostatic Body Fat Testing (Hydro-Densitometry):

According to research, "Hydrostatic Body Fat Testing "is still the "Gold Standard" to which all methods of body fat testing still compare themselves. However, the test is somewhat subjective because it relies upon the subject's ability to expel all oxygen from their lungs while submerged in a tank of water. Oxygen remaining in the lungs will skew the results. In clinical settings, this procedure is repeated a number of times, and an average is taken.

Advantages:

       The “Gold Standard” in body fat testing

       What other methods still compare to

       Fast test time (5-10 minutes)

       Most accurate technology available today

       Provides the best repeatability from test to test (tracking changes)

       Error rate around 1.5%

       Low equipment maintenance

       Has been the most accurate method for over 30 years

Disadvantages:

       Requires knowledge to administer test

       Being submerged underwater might be a little difficult for some (elderly)

       Must be able to blow out your air

       Does not necessarily take into account bone density / structure; merely water displacement

       Requires certain specialized equipment – generally not available at the local YMCA or gym; it seems to be more common on university or research facilities

Duel Energy X-Ray Absorptiometry Body Fat Testing (DEXA):

DEXA uses two x-ray energies to measure body fat, body fat percentage, muscle and bone mineral. One must lie down on an x-ray table while the machine scans the body. It takes the machine about 10 to 15 minutes to produce the image of the tissue. Today, this method is considered a gold standard because of its reliability, precision, and the fact that it is based on three body components (fat, muscle, bone) rather than two (fat and muscle) as in most other methods (including hydrostatic weighing).

 Advantages:

       Under proper conditions it provides accurate results

       Error Rate is less than 2% under proper conditions

       Radiation exposure is relatively low but it is still new technology

Disadvantages:

       Very expensive equipment

       Costly

       Uses X-Rays (which raises the standard radiation concerns)

       Not easily accessible, or mobile

       Different DEXA equipment can produce different results

       X-Ray license required to use machine

       Frequent testing may be of concern due to radiation exposure 

Caliper Body Fat Testing:

This is a small pinching device that measures subcutaneous body fat on your body. It has a +/- 3-8 percent error ratio based on technician skill, quality of caliper used, and number of sites pinched. Although it's quick and relatively easy to get it’s more of an estimate of body fat this is because it only measures a few areas on your body and not the whole thing. Plus, it is very subjective to each person that does the testing.

Advantages:

       Easy to use once skill is mastered

       Does not require much time

       Non-invasive method

       Inexpensive way of estimating body fat percent

       Portable

Disadvantages:

       Technical sources of error – did you measure the same spot? Are you sure? Did you change callipers? Calculation method? Etc.

       Error rate up to +/-8%

       Mostly concerned with subcutaneous fat (under the skin)

       May not be an ideal measurement for those who are obese, or very lean.

       Reliability is highly dependent upon skill, consistency of test location, and the type of calipers used

       "The analyzers are only as good as their equations" – This quote is also true of BIA methods; but I’m including it because it CAN have an impact on your readings if you don’t correspond to the type of person they calibrated the equation for.

Bio-Impedance (BIA) Body Fat Testing:

This measurement is done by hooking up an electrode to your foot or hand. An electrical low voltage impulse is then shot up one leg or arm and down the other to estimate body fat percentage. It measures the resistance in your body. Since body fat is a poor conductor of electricity, a lot of body fat will impede the current more so then lean mass. This grouping includes both Tanita AND Omron testing devices.

Advantages:

       Fast and simple

Disadvantages:

       Error ratio +/-5 to 8 percent

       Results effected by hydration levels, food intake, and body temp

       I’m repeating a specific from above - BIAs are extremely sensitive to the hydration levels in your body.

       Subjectivity is high

       Overestimates lean people and underestimates obese people

       Persons with cardiac pacemakers, electrocardiographs and/or other medical devices implanted in the body or used for life support should not use bioelectrical impedance devices – this is due to their use of electricity to do the reading.

       "The analyzers are only as good as their equations" – This quote is also true of callipers; but I’m including it because it CAN have an impact on your readings if you don’t correspond to the type of person they calibrated the equation / machine for.

Variations between tools:

Tanita: At one point I did research on the Tanita scales, because that was what was available to me, and I wasn’t sure it was telling the truth – and I found that typically, Tanita scales do lie about women in particular; especially those with a tendency toward pear shapes – it can provide a reading that is typically up to 7% off any of the other methods in my case, with a variance of over 5% sometimes in the same DAY; although it tends to be consistent with all other methods for my husband, both between readings and across equipment. Tanita claims their home line is +- 3-5% accurate; however I have found studies on line that report that accuracy for women is more likely  in the +- 5-8% range.

Omron: I personally have found that the Omron is more likely to be in line with what other methods report for body fat on my body, however they have a reported error margin of +- 4.1%.

How do I get my BIA to be as accurate as possible?:

Despite the pitfalls, you can take steps to minimize inaccuracies. Choose a BIA that's designed for your age group and fitness level. For example, several Tanita models feature an "athletic mode" that's calibrated for people who are involved in frequent, intense physical activity. If you need more information than what you see on the box, call the manufacturer's customer service department or check out their Web site before you buy. Also, follow the instructions precisely. BIAs are not toasters.  

When you start using your BIA, don't expect an accurate result from just one reading. Every BIA I’ve looked at recommends using its monitor for a week at the same time each day and averaging the results for a base line figure.                                                                                

Bod Pod Body Fat Testing:

This method tries to compare itself to the Hydrostatic method of body fat testing and it is based on similar principles. However, instead of using water it uses air displacement instead. This method has conflicting research reported on its results. Humidity, temperature, body hair and other environmental issues have been reported to negate the results of it's body fat readings. According to Georgia State University, if each body fat test is performed correctly to the recommended guidelines, there is a +/-3% error. Likewise, a study done by McCrory, etal.* the bod pod has a validity of .93 using hydrostatic weighing as the criterion measure body fat percentage. Medicine and Science in Sport and Exercise, 27 (12): 1686-1691, 1995

 Advantages:

       Fast 5 minutes

       Not difficult to operate

Disadvantages:

       Error ratio +/-3 percent

       Results effected by h body temp of muscles

       Hydration levels can effect results

       Body hair can have an effect on the results

       Very expensive equipment

       Breathing pattern might effect the results

       Can have an Claustrophobic feeling

Futrex Body Fat Testing:

This method of assessing body fat is based on the principles of light absorption, reflectance, and near infrared spectroscopy. This is an infrared laser that is shot into your bicep muscle that emits an infrared light which passes through both fat and muscle and is reflected back to the probe. The test results change depending on what you program into the machine. Hydration levels can also dramatically change the results of the body fat readings.

Advantages:

       Non-invasive

       Fast

       Convenient

Disadvantages:

       Error ratio +/-5 to 6 percent

       Results effected by hydration levels, food intake, and body temp

       Subjectivity is high

My personal experience:

I have been having fun trying to see if I can try out as many of these methods as possible, so bear with me here.  J

I have two BIAs (a Tanita and an Omron) at home; and just had Futrex testing. When working with a trainer, I usually request calliper measurements. This way, I have a sense of where I’m likely to be body fat wise based on if the majority of tests come back in a certain range. J

Let’s start with my measurements. I’m a 5’6” pear shaped female, who wears size 4 clothing; has a 27” waist…generally between 131 and 135 lbs (when someone asks, I generally answer 133 since it’s in the middle of the range I generally see.)

What do my body fat readings look like?

       Tanita in non athlete mode says that I’m 29%

       Tanita in athlete mode generally says between 20 – 22%

       Omron in athlete mode reads between 18.5% and 19.5%

       Futrex came in with 17.6% body fat

       Last set of calliper readings came in at 18%

So, to me, I figure that there’s a cluster of numbers that all end up below 20%; so if I average them together, I think it indicates that my probable body fat is actually somewhere around 19%. Conveniently enough, that’s pretty much that the Omron says, so I use that for my quick and dirty regular testing.

Take away:

All of these are useful methods; but they should be taken as indicators, and used to assess RELATIVE changes over several months. Other ways to assess progress, of course, include how you feel in your clothes (including body measurements), overall energy levels, performance in your sport or activity of choice, and attainment of your specific goals.

I find that what makes me the most comfortable is to use the Omron on a regular basis, and check in with some other method on a quarterly basis; just so I can see if the numbers still line up.

References:

http://www.getdunked.com/pages/default.asp?page_id=BPDHD35402&sid=OLZLW14019
http://www.baptistonline.org/health/library/spor5117.asp
http://www.mypharmacy.co.uk/health_products/products/o/omron/body_fat_monitors/omron_bf306_body_fat_monitor.htm
http://www.itinscales.com/fatscale.htm
http://www.halls.md/fat/bibliography.htm
http://www.tanita.com/QuestionsAboutBFMonitor.shtml
http://bootcamp.subportal.com/fitnesslink/exercise/bodyfat.html

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