That’s a question I get quite often inside of our coaching practice and rightfully so, it’s an extremely detailed and rewarding sense of metrics to change over time.
And when losing weight, it’s predominantly fat we want to lose. Therefore it makes a hell of a lot of sense to measure this so that we can see declines in BF% levels, without the decline in lean mass (muscle, organ, water, bone, etc…).
But how accurate are these body fat measurements, actually?
How often do fluctuations occur from test to test, really just making you feel like you’re working your ass off for weight loss to occur – but no fat mass to be burning off your body?
The unfortunate answer is not very accurate.
And trust me when I say, “I WANT these to be accurate.” Do you realize how much better I would seem at my job if these things worked perfectly? People would finally have the validation needed in order to trust the process and know that they are in fact burning fat and dropping weight (purely from body fat) every single week.
Yet when we factor in carbohydrate intake, stress levels and cortisol curves, water, sodium, how recently you trained, what you trained…. The list goes on, but when we factor all these constantly changing variables in as well, the tests are very rarely accurate and very rarely able to consistently show accurate trends, either.
In fact, based on meta-analysis on loads of body fat scan testing research (i.e. a meta-analysis is like a massive curration of up to tens of thousands of different research studies, pooled together to come up with mean results), the #1 way to actually read your true body fat levels is through a cadaver.
Yes, a dead body. This means that getting the truest measurement actually isn’t even possible because we’d need to cut into the human body and pull tissues from within to understand and determine where the level of body fat actually lies.
I know how frustrating that can be, trust me.
But that’s why in today’s blog, I’m going to dive into each of the most common body fat testing machines you can use. I’m going to rank them from least effective, to most effective. And I’m going to show you how to use each of them for the best results possible (some won’t even have much of an option there), while also giving you other measurements that may be much more useful inside of your fitness journey.
But before I do, I highly encourage you to read the blogs by Dr. James Krieger over at weightology.net. I’m a big fan of all things educational content and must give credit where credit is due – he was the first one to publicize the different research on all these body fat testing tools and he was who introduced me into the truth behind how they work, more like “IF” they work.
So if you want to dive into an even deeper approach for each of these, because he literally has separate articles for each device we’ll be covering today (excluding the inBody scanner), head over to his blog and get to reading!
So let’s dive in…
1. BIA’s (Bioelectrical Impedance)
The first and likely most inaccurate, happens to also be the most commonly used amongst fitness professionals, gyms and clients around the world – unfortunately. But it makes sense, it’s small and easy to store, cheaper than most, and can be used very quickly.
BIA uses an electrical current through your body, to read your mass levels. Fat-free mass (lean body mass) contains a lot of water, whereas body fat does not contain much water at all. Because of this, fat free mass will have less resistance to the electrical current running through your body, theoretically giving us a reading of your body fat levels.
Now, sounds great… but we run into some issues here:
→ An electrical current will follow the path of least resistance, which means if you carry a large amount of body fat under your skin it can pass right through it without even hitting or reading the actual fat tissues.
→ Fat mass and our ability to read it through bioelectrical impedance can be thrown off by the amount of hydration/water in the actual mass itself.
→ Many BIA machines have also been known and shown to completely miss sections of your body, which leads us to a reading that’s only based on a single section of the body rather than a total body fat percentage. It’s like an electrical signal going in one arm and out the other, completely missing your torso and down (where most body fat is stored in the first place, for most).
A BIA is estimation, at best. Sometimes it’s actually an estimation of another estimation, because it’s using different predictions from OTHER testing tools (this is how they actually create the device).
Lastly, let’s go over the margin of error so we can put the nail in the coffin on BIA: up to 8% range per reading.
8% “range” up or down tells us that we’re going to be way off when using a BIA to determine our fat mass!
And the really crappy part with this is that it’s not even an accurate tool for trends. By this I mean we can’t even argue to say that it may not be accurate, but it will accurately tell us which direction we’re moving – because maybe you care less about the number and more about the trend showing you’re actually losing weight, right? Totally get that.
But it won’t even do that because the hydration levels of tissues and fat mass change over time, specifically as we change our body composition – lose fat/weight, add muscle. So it will consistently throw it off in a wide range, making even the trend pretty inaccurate.
It’s a Russian Roulette Body Fat Scanner.
2. Skinfolds / Calipers
Skinfolds and calipers, the classic tool for measuring body fat. Why trust a machine when we can use our hands and actually do it ourselves, right? Wrong.
Machines can be pretty damn precise, that’s why we use them for pretty much everything nowadays.
But not so fast, maybe there is some merit here…
When using skinfolds, we can consistently see trends moving in a specific direction if we completely control all other variables.
What this means is that if we want to use them for measuring and tracking our body fat percentage over time during a fat loss phase, we need to mimic the exact setting in as many ways as possible.
Example: first thing in the morning (between 7-8am), every other Saturday, after about 6-7 hours of sleep, following a normal dietary day (non-refeed), without changing training up the day(s) prior….
Are you catching my drift? THE SAME. All of it. And as meticulous as that may sound, it’s what’s going to allow accuracy so we can avoid water retention and weight fluctuations.
And this way will not be overly accurate. I remember using this for my physique show, when I got down to 4% bodyfat. See picture below:
As cool as it was for me to see 4% on the caliper measurements, that wasn’t realistic. I was still lifting weights and honestly could have squeezed another few lbs. of fat out of my glutes and lower belly. 4% is damn near death, if we’re being realistic here.
My guess is that I was more like 7%, at best. But it did give me a consistent trend as I moved down from around 13% to that 4% we saw on stage.
Now, this all sounds amazing… however there’s still some downfalls with calipers:
→ This is very much determined on how delicate the readers hands are and how easily you can pinch the skin. Everyone has different skin thickness and subcutaneous fat levels, which change body part to body part. All of this simply makes it to be exact when pinching skin with fingers, over a long period of time. Because of this, I recommend doing it 3x and taking the average on each point.
→ The equation can differ person to person. Again, individual variance changes things in so many ways and when using an equation that was designed off of THOSE specific individuals… what makes use think it will match us perfectly, as different individuals? We may get lucky, but we may not. The equations to use after the measurements are taken were created off specific gender, age range, body type, etc… and all of those things just throw too many wrenches in the mix.
→ The equation used, just like the BIA actually, was built off of other predictions. It’s a prediction of another predication. They used research and results from hydrostatic weighing to determine how they get these results, but even hydrostatic weighing can be up to 5-6% off on individuals (we’ll touch on this tool next). So we’re using an equation that’s an estimation of a prediction… not very reliable.
The sad news here is that the error rate can be up to 15% on any individual and as low as 6%. So it’s a big margin of error, however; it can be accurate when looking at trends – so when using it, don’t pay attention to the number itself, but the trend downward instead.
3. Hydrostatic Weighing & BodPod
Hydrostatic weighing was known to be very accurate, but quite uncomfortable because you’re dunked into a tank/ball of water while it measures your body mass.
For anyone who doesn’t like water or has Closter phobia… skip this method and keep reading!
When you’re dunked under, it measures the amount of water you displace, which then gives the readers your total body volume (how much space your body takes up).
So what does this mean? How does this tell us anything valuable?
Lean body mass (fat free mass) is more dense than body fat, so it weighs more for a given amount of space. Also, fat tends to actually float in water, while our lean mass will sink. They can use these to calculate your body density. From that amount, they can estimate your fat and lean mass.
THAT is how hydrostatic weighing works; whereas the BodPod does the same exact thing while searching for how much air you displace rather than water.
The main 2 reasons this is flawed is because, first, our body holds water in other tissues, the lungs, the digestive tract, etc… which can allow us more floating potential, throwing off the ability to read an accurate measurement.
Second, is because the equation is another estimate-based calculation that just has a lot of room for error. The equation predicts that fat-free mass has a certain density to it, but this can change depending on multiple factors per person – your ethnicity, for example, can change the density to your fat-free mass. Also, your weight fluctuations over time (fat loss, muscle gain, weight changes) can change your fat-free mass density, once again throwing off the actual reading of the test.
In groups, the margin of error is actually only 1-2.6% – so really not that bad.
But in individuals (we’re not pooling together averages, here), the error rate can be as high as 6%. Meaning it could read you 20% body fat, but you could actually be 14% or 26%… that’s a bit large to give me comfort, as a coach.
So although this reading may be more accurate when the calculation factors in your ethnicity and all other possible changes to fat-free mass density AND when we’re averaging groups of people, the room for error can be large with individual participants and when we’re tracking over time – which makes it an unfavorable option to use.
Ahhhh the inBody machine! One of the latest and greatest machines, which has picked up a ton of popularity in the last 5ish years.
So how do these inBody machines, work?
An inBody machine uses a direct segmental multi-frequency bioelectric analysis method (DSM-BIA), which measures body composition by sending multiple electrical voltages through the inner body, resulting in up to six different impedance readings for the truck and four limbs.
The great news for you, is that we don’t need to overly explain this one – because we already did? An inBody machine is like a very big BIA scanner that you stand on and hold, making the electric current more accurate because it sends through your feet and hands.
Instead of holding it and making the possible error of not allowing the current to fully run through your entire body, you can use an inBody and get that current to actually pass through more than just arm-to-arm.
So although this may be more accurate than the hand held BIA, it still runs into the exact same problems and margins of error – just on a slightly smaller scale.
This also makes it inaccurate for repeated use, hoping to see trends in any one way.
I’ve personally seen clients get frustrated from this, using these machines time and time again. I’ve watched result-charts show clients losing muscle, maintaining fat mass, and dropping total weight… while progress pictures look dramatically different (improved) and biofeedback increasing (improved).
5. Fit 3D Scanner
If you haven’t seen an inBody, you may have seen a Fit 3D Scanner – both look very similar, but use slightly different technologies.
I actually very recently was invited to use a DEXA machine from the company (that’s the last on this list, being the most accurate) but they also owned a Fit 3D Scanner and offered me to do both… so why not?
On the 3D Fit Scanner, I was 20.2% body fat.
On the DEXA scan, I was 13.3% body fat.
Both tests were done just minutes apart…. Odd, right?
The reality? The DEXA was probably pretty damn accurate as I’m very familiar with what 10% vs. 15% bodyfat on a male body and I was absolutely in between when doing the test.
But 20.2%? Far from where I normally sit, as I wouldn’t even be able to see my abdominals in the morning at that point.
So how do these work? They take a very detailed 3D scan/photo of your entire body and then use an equation to produce an estimated body fat percentage and lean tissue mass total.
Unfortunately there isn’t much research on this, so we don’t have an actual percentile of error to give you, but as you can see from my experience… it’s pretty big, a guarantee of about 7%.
The flaw? It’s another estimation-based calculation, from predictions of other individuals inside of testing strategies. Therefore simply not reliable for individuals looking to get real answers to how much fat they carry.
The only thing I will give to this machine is its ability to see weight distribution and posture analysis. But that’s a given, you step on a scale and take a half-naked picture. How wouldn’t they be able to analyze those two factors? My point is that it’s nice to KNOW what those two factors, are.
I saved DEXA (Dual Energy X-ray Absorptiometry) for last, because its absolutely the most accurate.
The main issues here? It takes longer, it’s more expensive, and you typically need to go out of your way to find one.
Is it worth it? Absolutely, if you want to know your body fat percentage – at least the closet reading to what it may be.
DEXA is a 3-compartment (most of the others are 1-2) reading that can determine fat, bone mineral, and all other fat-free mass that does not include bone. Because of this, it is more accurate and has better understanding over what it’s detecting.
The best part of DEXA is that it does rule out a lot of those error rates seen before AND because it was built and continues to be a big piece of the medical community and furthering technology, it advances and improves as the years go on. So the future for DEXA is promising.
But, like the rest, there are still some flaws to the DEXA:
→ The biggest one being differences in settings and manufactures or operators. This simply means that when you get a reading; make sure you repeat it in the same exact place, with the same people, and on the same exact setting. I know of a personal friend who RUNS these machines in his labs and he’s seen massive errors on these, simply from using a different setting on the reader one time compared to another.
→ As always, water and food volume can possibly play a role. The room for error is far less, but it’s still there. So it’s important to use DEXA under all the same variables as before, meaning you should eat the same, train the same, date/time it the same, and sleep the same, going into this machine.
→ As before, fat-free mass hydration can vary and change over time and that can be another source of error for this reading. It’s important, as I just mention, to control all things that can dictate or fluctuate your hydration levels when going into this machine. A change in hydration alone can change your body fat reading by nearly 3%, when it’s in fact just water!
DEXA, like the rest, still has a margin of error; it sits at about 4% in some studies and upwards of 8-10% in others.It’s been found that size, gender, fatness, disease, and more can affect this, though.
This tells us that the healthier and leaner you are, the more reliable these readings will actually be – likely because there is just less things that can affect the test results. In fact, a study on bodybuilders was MUCH more accurate than the studies done on regular individuals.
In-group settings, error rates are small. In individual settings, they can increase quite a bit from what research has shown.
The conclusion here is simple, DEXA is definitely the best from what we can tell but it can never paint the exact picture because there will always be variables from person to person that can throw off the reading.
So if you’re going to use one, use a DEXA and use it every 3-6 months while controlling all the variables you possibly can and going to the exact same place to take the test.
Lastly, make sure that you’re more focused on the trends and not the exact % it reads.
Inside our coaching practice, we use metrics – a lot. Because metrics give us actual data that can truly tell us what’s going on with someone.
But we don’t typically use body fat scanners, for all of the reasons above.Instead, we use the following:
→ Daily and Weekly Weigh In’s
→ Training Performance
→ Body Measurements (Tape Measure)
→ Macros and Calories
→ Biofeedback (Sleep, Stress, Motive, Hunger, etc.)
→ Visual Appearance
Our clients get amazing results, without relying on body fat scanners to tell them how successful they’re becoming in their own personal fitness journeys – and even with the clients who DO use things like a DEXA scan, we never remove those concluding metric points because they tend to outweigh any other form of metrics you can use.
Cody McBroom is owner and head coach of Boom Boom Performance. He’s a Strength Coach and Nutrition Expert located in Seattle WA. He coaches people in person and online, now internationally. His passion is helping individuals changing their lives through body composition transformation, as well as creating content across all platforms to help individuals and other coaches learn more about training and nutrition.