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So everyone is talking about Mattdoesfitness at the moment for various reasons, as he prepares for his entry to bodybuilding. One of the things though that keeps coming up is that he says a number of things about his body fat. Matt had his body fat tested with a DEXA, and he came up at 16.9%. His brother Ben got his tested at the same time and came up with 21.2% body fat. As a result the two have gone on a cut to try to shred some of the excess. They have also been talking about it on all the social media and YouTube channels and podcasts. Some of the things they are saying are ‘I just have less fat on my abs, but it’s hidden elsewhere’, ‘I’m much fatter than I look’ and so on. Of course both experts in the field as well as casual observers have been questioning the result, but with a fully documented process, and using the gold standard measure of body composition, the result seemed unassailable – or is it? 

Why does My Vital Metrics need to weigh in on this?

One of the reasons we’ve not written about this till now is because of the obvious financial interest we have in this. After all, we run a competing DEXA body composition lab to the one Matt used. We must emphasise that that lab has not done anything wrong, it has conformed exactly and continues to conform to manufacturers’ recommendations. The issue lies in the science.
However, we have found people who are wondering “well if Mattdoesfitness is 16.8% and looks like that, then what the hell am I?” There is also the case, if we take in the same video his brother, who measured in at over 21%. Now here we have a real issue because the recommended body fat for a man is between 8 and 20%. So Ben Morsia, who is also an extremely fit and healthy young man has now been told that he is carrying an above-healthy level of body fat. Given what we’re about to discuss below – we don’t think this is acceptable for the public understanding of body fat, and so some further information in the area was needed.

What are the key aspects of a DEXA calculation?

The key thing you need to know about DEXA is that there are two type of calculation used in the final result. These are called NHANES and Classic. The Classic calibration uses the unedited data that the DEXA has actually measured. It is the standard calibration that lead to DEXA becoming the gold standard measure of body composition for the last 40 years. The classic calibration accords with and reinforces all the body composition science that preceded it also, including the gold-standards of the time which included callipers, the Bod Pod, and Hydrostatic weighing. The other calculation, NHANES, for reasons I will go into, actually takes a DEXA scan, and then performs a further calculation. It reduces your lean mass by 5.4%, and then adds the figure that was removed from lean mass to the fat figure to make your overall weight correct. If this sounds a bit unusual to you, as a scientific process, we agree, but there’s an explanation below about how this came about.

So What are Matt and Ben’s REAL Figures?

Now which calculation do you think led to Mattdoesfitness getting a reading of 16.9%? you guessed it – it’s the NHANES calculation, so that scan will report his body fat as up to 5% higher than he actually has. So what’s the reality? Based only on the information in the video, it says he’s 16.9% with a total fat mass of 16.7kg. By our calculations, that means a total mass of 98.81kg. Now we have to make an assumption about Matt’s bone mass as this is not in the video, if we assume a bone weight of 3kg – which would be heavy bones, then that leaves us with a lean mass of 79.11kg. Reversing out the calculation for NHANES is as simple as dividing the lean mass by 0.946. So that means that Matt’s real body fat percentage is 12.3% as correctly measured by a DEXA, and working to the same standards as everyone in the fitness industry expects. Ben is around 17.1%. Once again the difference this makes to an individual and to their plan is huge. I will cover this below.

How did this situation come about?

Back in 2005, the massive US study the National Health and Nutrition Examination Survey NHANES was about to get started, and they needed to choose a method for measuring people’s body composition. With hundreds of sites across the US, they chose DEXA, but more than this they needed to ensure all DEXAs were calibrated the same, so they did a small pilot study to establish a calibration. In a 2005 paper by Schoeller et al, they compared 6 datasets which compared Hydrostatic Weighing and a Total Body Water method to DEXA, and they found, according to the study, that “DEXA overestimated lean mass….” Schoeller’s recommendation was therefore to use DEXA, but to reduce all the readings’ lean mass to 94.6% of the original reading, and therefore to increase the fat mass accordingly. The NHANES study accepted this paper and implemented this calibration. It then became the ‘standard’ calibration for the NHANES study, which was big enough that it in turn became the default setting on all DEXA machines for quite some time.
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What are the problems with this method and approach?

Now there are a huge number of problems with this approach and with the underlying study that led to it. To start with, of the datasets used, 5 out of the 6 were never published. Secondly DEXA had already proven itself as the gold standard time and time again, beating out hydrostatic weighing and all other methods for the most accurate body composition figures – and has continued to do so in the time since. Lastly, it’s just such a fudge. DEXA goes pixel by pixel to build up a picture of your body fat, bone density, and lean mass – and to just arbitrarily reduce this figure, uniformly around the body to conform to a single figure got by another method is just so sloppy.
The biggest issue however, is that it completely went against all body composition science which has been done since the 1950s… These general rules of thumb that men need to be around 10-12% to have visible abs didn’t just come from nowhere – it’s consistent with what trainers have seen of their clients’ body composition since then. The NHANES calibration goes against all of that, and claims that someone with 17% body fat can have abs ‘just because the fat is in places you can’t see’ – but it’s just not true.

So it was the scientific standard?

Not exactly. It had to be used for the NHANES study in the US specifically – which was vast and collected more information on body composition than any other has in history. Outside of this however it’s a more complex story. Many of us in the industry and close to it never adopted the NHANES calculation, and eventually the chorus of scientific papers which came out in response has proven overwhelming. In the end, Hologic, the leading maker of DEXA Scanners for body composition, came out and issued its official guidance that repeated studies have shown the classic calibration is definitely going to give you the most accurate results. Their recommendation is therefore that all new studies should use the classic calibration. You can read the entire paper they produced here, https://hologiced.com/wp-content/uploads/2020/09/Hologics-approach-to-calibration-for-body-comp_Kelly.pdf though we’ve highlighted a couple of paragraphs here:
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A few percent here or there – what does it matter? 

Actually it matters a lot. If we take Matt’s figures. If we were to accept 16.9% – there’s certain actions that we would advise if people wanted to get leaner. Above 15% body fat for males (25% for females), there is still a likelihood of some insulin resistance. It’s enough that tightly controlling more insulin through carb reduction, careful meal timing etc. may be a good strategy to help the person cut further. At 12.3% we can be fairly certain that insulin is well under control, and so we would be looking to maximise the use of carbohydrates to fuel workouts appropriately. Similarly it could affect what people choose to do next. We would not recommend someone who was really at 17% to commence a bulking phase (if they wished to go through bulk/cut cycles) – it’s just too likely that the bulking will be inefficient and put on more fat. At 12.3% however, that’s a completely different story. 

Similarly for Ben. There’s a big difference between prioritising fat loss as a health concern (which we would for a young man over 20% body fat) and telling the person they are healthy as they are. If they want to change for aesthetic or lifestyle factors, that’s a different thing. It can not only affect the plan, but more importantly can have the potential to create real anxiety and concern in the client. 

I’ve had a DEXA Scan – how do I know if it’s the NHANES Calculation? 

If you took your scan in the UK, and not with My Vital Metrics, then chances are you’ve been given an NHANES calculation. If in doubt check your report – you will see the NHANES BCA tag on the report itself, like below

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I’ve had an NHANES DEXA? How do I get my real body fat?

If you’d like to calculate your real body fat percentage, just grab your NHANES DEXA report, and plug some key figures into the calculator to the left – it will calculate your real DEXA body fat %

Once again, DEXA scanning services have not done anything wrong in choosing the NHANES standard. Further, the manufacturer recommends that if a facility has started a study using NHANES, then they should continue. It would be a problem for any facility to switch standards and keep consistency for their clients. 

Of course if you’re interested in your real figures going forward we’d recommend then re-baselining with My Vital Metrics, so that you can get your real body fat figures from this point forward. 

It’s important to know that each DEXA is uniquely calibrated also, so no two DEXA machines will be exactly alike. However My Vital Metrics is the only publicly accessible facility in the UK which calibrates to a Whole Body Phantom – this is a precision tool which contains a fixed and known amount of fat, bone, and lean mass. By scanning this regularly we are able to see and correct for any discrepancies in the testing. If we found that our machine was drifting or reading figures on the phantom which were not correct, we would cancel all appointments until it was fixed and recalibrated.

As we said, this is a very specific research-grade process and My Vital Metrics is the only facility in the UK who ensures the ongoing accuracy of our machine this way. 

If you’ve any questions or concerns about your past scans, or anything we’ve raised here, please don’t hesitate to get in touch.