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Body fat and body composition analysis

I have been looking into some equipment for analysing body composition recently.  What it is for really is something to check how much of your weight is fat and how much is lean muscle.  Why is it important? Well these values can give us important information that can assist in understanding everyone as an individual.  How much fat we have affects day to day function as well as sports performance.  Our fat stores can be too high, and less commonly too low, both of which will impact performance and can impact your health.

We also want to know how much of us is lean muscle because this affects how much energy we use and thus how much energy we need from our food.  Fat is metabolically inactive so we don’t want to feed it and understanding lean muscle stores allows us to estimate calorie needs better.  Added to this is the benefit of monitoring the gains in lean muscle associated with exercise and training.

With any weight loss or weight gain programme we can monitor what type of tissue is changing. Are we losing fat or losing muscle, are we putting on muscle or adding fat?  Even when our weight does not change we may still be losing fat and increasing muscle stores.

To know, we need to measure.

There are a number of different ways of measuring body fat and lean muscle.  The only 100% accurate method is with a cleaver and scale on the autopsy bench but this is not very practical.  So man and his science have come up with a number of indirect measures.

The most accurate of these, giving us about 98% accuracy are dual x-ray absorptiometry (DXA) and magnetic resonance imaging (MRI).  Both are pretty damn pricey and require large immovable pieces of equipment.

The next best is underwater weighing which is self-explanatory really. The accuracy of this is about 97% but it is quite uncomfortable and nervy for us non-swimmers.  You are obviously submerged in water, exhale every last ounce of air out of your lungs and then wait a while so the displaced water is measured. This equipment is also pricey and immovable and is usually only used in laboratories for scientific purposes.

Air displacement works on a similar principle measuring displaced air instead of water and is quite accuratetoo.  The unit (known as the BOD POD) is not readily available and quite expensive too.

Bioelectrical impedance analysis (BIA) is a more common tool in the health and fitness industry.  It is easy to use, portable and relatively inexpensive.  It works on the principle that body water conducts an electrical current and by measuring the resistance of this current we can measure the proportions of body water which is equated to lean muscle stores.  Although easy to use, the validity of the tool is questionable and variance is high.  Readings are affected by the time of your last meal, your hydration status, caffeine intake etc.  New equipment is now on the market that uses multiple frequencies and provides more accurate results but with a longer price tag. The same limitations are present but minimised.

Skinfold callipers are also used in many field studies and measure thickness of skinfolds at certain sites.  This provides a measure of fat stores under the skin at these sites, the sum of which are then plugged in to an equation to determine total body fat stores.  Many years of research and large populations were used to validate these measures and equations against the “gold standards” of DXA or MRI.  The callipers themselves are reasonably inexpensive and portable but the actual technique of measuring requires training and experience and large variations are common for this reason. For the chap being measured it is also quite uncomfortable being pinched at any number of sites to get these measures.

Ultrasound devices use the same technology as similar imaging tools to provide a visual of muscle and fat layers as your doctor would to show a muscle tear or to see development of a fetus during pregnancy.  Fairly new to the market it is an interesting tool that not only provides a visual of the fat layer, but also the quality of muscle underneath.  The device is used in place of the skinfold callipers to measure at the same specified sites. The results are more accurate because human error is reduced.  The same validated equations are used to determine total body fat. The device has been validated against other tools such as underwater weighing. One study on validation against DXA is ongoing. I may be punting this one a little but it interests me and yes I have ordered one. Check out this site

When this bad boy arrives I will be completing my repertoire for a full health assessment.  This will include a full nutritional analysis, clinical screening for blood pressure, cholesterol and glucose and now a complete body composition analysis with weight, height, fat distribution and body fat. Get in touch if you are interested.

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7 Responses to Body fat and body composition analysis

  1. Jannie van Zyl Mar 9, 2015 at 12:52 am #

    I found a place that does DEXA Scans in Cape Town after a really long search:

    • Food For Sport Mar 9, 2015 at 7:58 am #

      Thanks Jannie. If you have one done please pop me a mail to let me know what your experience was like if you don’t mind?!

      • Jannie van Zyl Mar 9, 2015 at 8:04 am #

        I did do it. Takes a few minutes. You just lie on a bed and the machine scans you from head to toe. It makes a few passes.

        My total fat % came back as 13%. From the various photos you get on the internet showing fat %, I actually thought I was closer to 10%, so it was a bit of an eye opener.

        I drove directly to Virgin Active to measure with their machine and it said 19% and then home where my bio-impedance scale said 22%!

        One of the coolest things is that it gives you your visceral fat, the scary stuff in your belly that’s linked to many diseases such as Insulin REsistance, CVD and stroke. Mine was measure at 100g, so I’m pretty happy! 🙂

        I’ll definitely do this twice a year.

        • Adrian Penzhorn Mar 9, 2015 at 11:12 am #

          Thanks Jannie. Great to know. If you are in the Constantiaberg area I would love to see how my ultrasound weighs up against your reading so if you have a moment free in the next week pop in.

  2. Jon Littell May 26, 2015 at 12:42 pm #

    Living in north Joburg for a few months and I’d really like an accurate scan. I can’t seem to find a DEXA scan nor a Bod Pod in the area! Cosmed (the bod pad maker) lists a biokineticist in Sandton, but they don’t actually have the machine. 🙁

    Anyone know of a resource?

    • Food For Sport May 26, 2015 at 1:03 pm #

      Hi Jon
      I am not sure but your best bet for a DEXA would be an academic hospital or bone health clinic.

      • Jon Littell Jun 7, 2015 at 11:47 am #