8.  Body fat measurements 

Fat loss rather than weight loss per se is the goal if you are trying to reverse diabetes and lower your cholesterol.   Unfortunately measuring your fat content is not so easy and the only sure way to check your exact body fat percentage is posthumously by dissection.  As that seems a little extreme, other less intrusive measures can be used to give an estimate of the fat level! 


The simplest qualitative measure is looking at yourself in the mirror.  This costs nothing and tells you almost everything you need to know  but if you want to be a bit more scientific, there are techniques such as underwater weighing, the bod pod, and Dexa scans that will provide very accurate measurements.  Unfortunately these are expensive and not at all suitable for use by individuals trying to track how much fat they are actually losing on a week to week basis.


There are a number of measures or indices available that attempt to categorize fat levels of individuals based on data gathered from large populations.  While these indices can be very effective when interpreting how fat levels change in large populations, they can be misleading or inaccurate when applied to us as individuals.  That’s because gathering data from large populations inherently involves an averaging  of component parameters such as bone density, lean muscle mass, and stored fat, and that average is an inherent or implicit part of the index that is created.  If your body type corresponds to the implicit “average person” which underpins the data then it may well be accurate for you, but it could also prove significantly inaccurate in categorizing you as normal or over weight.


8.1 Body Fat and the Body Mass Index

The common measure we all know about is the Body Mass Index, or BMI, which was originally designed only to study how the mass of a large population varied with the square of the individual height.  As such it has the units kg/m2.   Although it was never intended for use with individuals it has come in to common use to indicate whether we are normal/fat/obese, despite the fact that neither of the two parameters it uses are a direct measure of your body fat percentage.  When I started visiting the gym regularly over twenty years ago the regime of cardio and weight training soon had my waistline reducing noticeably as I lost fat and added muscle.  My belt had to be tightened another notch but what happened to my BMI?  Well, according to my BMI score, I had gone from being a normal healthy weight to being overweight!  That’s because I had added muscle which is slightly more dense than fat, my net weight increased, and the simplistic approach of the BMI assumed that extra weight was fat.  Not very helpful or accurate.


So what does the BMI say about my current body composition?  I am 68kg and 1.74m tall so my BMI is therefore 22.5 kg/m2 which actually sits above the middle of the “healthy” BMI range of 18.5-24.9.  So even although my ribs are now clearly visible, and if I squint I can see the outline of my abs and obliques, the BMI would say that I am still above the middle value of 21.5, which is presumably considered the optimum level.  That’s because the BMI does not recognize the muscle mass or bone density that I have added since losing the fat.  As an individual I do not conform exactly the profile of “Mr Average” that is inherent in the underlying population data, and in fact very few individuals will ever conform.


Worse than that, let’s look at the lower limit of the  “healthy” BMI range which is defined as 18.5kg/m2.   My body fat is 8.3% so I have 5.6kg of body fat.  A BMI of 18.5 would require me to drop to a weight of 56kg.  Even if I lost all of my remaining body fat (which would be very dangerous as we all need a certain amount of essential fat) I would still be 62.4kg!   I could not reach 56kg without losing all my fat and a load of lean muscle as well!   So while the BMI may consider 18.5 to be healthy (just), it would be a very unhealthy target for me to aim for.   That’s why I completely ignore the BMI, although I do recognize its value in characterizing large populations.


8.2  Body Fat and Waist to Height ratio

What about other indirect measures of body fat?  Dr Mosley refers to “Waist to Height” as being an important indicator of visceral fat – the nasty stuff that lies below the surface and surrounds the pancreas and liver.  The waist measurement is not your trouser size!  It is measured at the minimum circumference which lies about an inch above the navel and we should aim for a Waist to Height ratio below 50%.  From what I’ve read this does appear to be a well validated measure of future health, and of course it’s endorsed by Dr Mosley so it must be good!


8.3  Body Fat and Waist to Hip ratio

There is a related ratio that some claim to be even better than Waist to Height and that is Waist to Hip ratio, but a trawl of the internet shows quite polarized opinions on this measure.  For a male the healthy range is defined as <90% and for a female><>  In my case, however, even although my body fat has dropped from 29.5% to 8.3%, my Waist to Hip ratio has remained almost unchanged at 90.2%.  So the Waist to Hip ratio does not recognize the 19.6kg of fat I have shed.   I think this index may depend quite heavily on your body shape.   In my case the fat was fairly evenly distributed across the whole body and my belly/waist was not particularly prominent or protruding.  So when I lost fat it disappeared from both the waist and the hips, and the ratio remained virtually unchanged.  Of course someone who is more pear shaped might have a completely different result.  Unlike the Waist to Height ratio, which has only one variable, the Waist to Hip ratio has two variables and they are not independent.  As a mathematician and engineer that sounds like an inherently flawed measure to me so I have stopped measuring it.


8.4 Measuring your body fat in practice

So how have I determined that my body fat is 8.3% without resorting to dissection? Initially I went for body fat composition scales and I used units from both Omron and Tanita, the latter being particularly expensive.  Yet in spite of the high cost of these units I would describe them as worse than useless.  The Tanita offered an impressive array of body composition analysis with a breakdown of total fat, visceral fat, and muscle mass, as well as breakdown by body area.   It does produce lots of readings but unfortunately the readings varied by so much on any particular day and from day to day that I had no confidence in any of them.  The manufacturers tell you to take readings at a consistent time of day and not after exercise or showering, which I did but to no avail.  I would regularly find that my reported body fat had grown or shrunk by several kgs in the same day or from day to day and that’s just not possible.  So don’t waste your money!  These scales promise a lot but in my experience are useless.


There is however a much cheaper low tech solution that actually works.  Just spend about £30 on a set of digital body fat calipers and a tape measure and you can perform reliable repeatable measurements that track your fat loss and waist reduction progress.  This is the device I used : https://www.ebay.co.uk/p/AccuFitness-FatTrack-Gold-Premium-Digital-Body-Fat-Caliper/22012040215


With this devices you pinch your skin in three places (pecs, belly, and leg for a man) and the device estimates body fat composition from the measurements you’ve made.  From my investigations it would appear that calipers, utilized  skillfully,  can be almost as accurate as Dexa scans down to about body fat levels of 15%.  At very low body fat levels their accuracy decreases because there just isn’t much skin left to pinch.


The perceived wisdom also appears to be that they are difficult to use and practice is needed to be able to obtain consistent results.  My experience has been completely contrary to that.  After a couple of days I found I could obtain repeatability of ±0.1% over three consecutive readings and that is way more than anyone needs.  I take measurements once a week :  always as soon as I get up, and definitely before showering.   Using the calipers after showering or a session in the gym will produce errors of 1-2% because the skin elasticity is affected by these activities.   The look up tables and algorithms used in the device are of course based on large population studies and require the gender and age of the person to be entered but, in contrast to BMI or other indirect measures, skin fold calipers are directly measuring a parameter that is dependent on your individual fat level.


8.5  My body fat changes after six months on 5:2 + Mediterranean Diet

At the start of my diet I weighed 85.5kg and my body fat composition was 29.5%.  I knew I was a bit overweight but one third of my body was fat!   After six months my body fat is stable at 8.3% but I have also added some muscle through weight training.   So how much of much fat have I actually lost?  The calculation is quite easy :


My initial fat level was 29.5% so actual weight of fat = 0.295x85.5 = 25.2kg.

My final fat level was 8.3% so actual weight of fat = 0.083x68.0 = 5.64kg.

Hence the net fat lost = 25.2-5.6 =19.6kg (43.1lbs).


Also, since my final weight was 68kg that means my net weight loss was 85.5-68.0 = 17.5kg, hence the muscle gained through weight training = 19.6-17.5 = 2.1kg.