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I recently got the results of a few body composition tests on one of those devices where you stand on some electrodes and hold a handle with electrodes while it passes a small electric current through your body. These are called Bioelectrical impedance analysis devices (BIA).
Here are the results from the three tests I took.
There are a few things you will notice
It's all in German, but I will point out what you need
Between the three tests, I lost 1% body fat (BF) and gained 500g of muscle (Pretty good going)
They were all taken with 4mins…..
*Also, I am almost certainly not as low as ~12% BF
Now, I am fortunate to have access to one of these where I can take multiple tests, but normally, when you are offered a body composition test, you only take one measurement.
Imagine that I took these a month apart to see the results of my hard work, training and dieting and came to the conclusion that, yes, the approach I am taking is working and I should keep on doing this (1% less BF% and 500g of muscle would be a great result from 1 month). In reality, I hadn't made any progress. Or worse, imagine if the error is actually going the other way, and after a month, I retest and come to the conclusion that what I am doing is not working when, in reality, what I am doing is working really well.
The inaccuracy you see with my results is not just a one-off…this is an inherent problem with this type of body composition test.
One study found that this method of testing underestimated most of the participants' body fat levels (not total weight, just body fat) by 8lbs (~3.6 kg) and many of the participants by over 10lbs (~4.5kg) after a 6-month weight loss period when compared to a more accurate test.
Another study on bodybuilders (who usually have a more consistent diet and training routine than the general population) found that the BF% had an error of up to +/- 8%.
To give you an idea, say someone’s test said they are 12% body fat, which is considered “beach lean” for a male, muscle definition, 6pack etc. 8% less would equal a BF% of 4%, which for a male is putting you at serious medical risk and is only achieved for a very short time by some bodybuilders. This would probably be the leanest person you will ever see and most people have never seen someone that lean in real life. 8% higher than 12% is 20%, this is what I can “fluffy”. No abs, maybe some muscle definition if you are quite muscular. This a “dadbod” but not chubby enough to have a gut.
BIA devices cannot reliably tell the difference between these levels of BF%. You might be saying to yourself, “Well, if I was beach-lean and either got so lean that I was at risk of winning a bodybuilding competition or got a dad-bod, I'm pretty sure I would know which way I had gone”, and you would be right.
These are just a couple of studies as an example, but there are 100s, some even showing greater margins of error.
Most of the time, using progress pictures and maybe a few skinfold or circumference measures, you can more accurately access changes in your body composition than with these devices.
Why is this? Because these devices are not actually MEASURING BF% or any of the other numbers they give you, they are just ESTIMATING it. The only way to truly measure BF% is by dissecting and melting you down, which is a pretty final sort of test.
What BIA devices do measure is the level of impedance they get when passing different electric currents through your body. Impedance is a similar concept to resistance and basically tells us how well the electricity was conducted by your body, and this is dependent on how hydrated the different tissues in your body are.
Muscle is generally more hydrated than fat and, therefore, conducts the electricity better, so the device assumes that if the electric currents pass through more easily, then you have less fat and more muscle and other well-hydrated tissues. But so many other things affect your body's impedance.
For one, how well the electricity makes it from the electrodes to your body could be affected by the thickness of the skin on your hands and feet as well as the moisture between you and the electrode. This is what I think threw off my measurements on that day. I think between the measurements, which each take a couple of minutes, I was getting slightly clammy, holding my arms out to my side, standing in a warm room. This would cause me to conduct the electrical currents slightly better, with less impedance, and therefore, the machine might assume I had more muscle and less fat.
In case you were wondering, I took all the recommended precautions of fasting before, not exercising for a certain number of hrs before, being “normally” hydrated and using the wet wipes that come with the machine for cleaning your hands and feet and improving your contact with the electrodes.
These are the recommended precautions because how well hydrated you are, what foods you have eaten, and the localised swelling in muscles caused by exercise can all throw the device off as well.
You may wonder then why BIA devices exist. In research, they are used because they are relatively accurate at estimating GROUP results. If, on average, it estimates that a group of people lost 5% BF, then on average, the group probably did because all of the inaccuracies and other factors that can affect the estimated average out.
But you probably don't care about what the average result from everyone in your gym is, you care about what your results are to assess if all the hard work you have put in is doing what you want.
So when BIA devices are used to give individual results, like at the beginning and end of a 6-week challenge or something, they are more of a gimmick to give you some numbers to look at than anything useful. In fact they are not just not useful, but as you can see from the size of the errors we discussed above, they can actually give you completely the wrong results pointing in the wrong direction!
Nothing is more frustrating than doing a diet, feeling like your clothes are feeling better, you seem to look leaner in the mirror, the scale weight has come down, and then you see the results of your BIA test, which you assume is accurate and it says that you have actually gained body fat….
So what should you do instead? Precisely what I just described above. Often these simple metrics do a much better job of assessing changes in individuals.
Do your clothes fit better?
Clothing is just a piece of material with pre-set circumferences on different areas of your body, so using clothing or actually measuring circumferences with a tape measure is a really good tool for assessing changes in body composition (If you would like a full guide on how to take and interpret body circumference measurements contact me and I will create it as a future post).
Progress Photos
Progress photos are a great tool for assessing changes in your physique, because they are directly assessing change in your physique. Do you think you look better? Are the areas you want bigger looking bigger, and the areas you want smaller looking smaller? Then great! That all that matters, with the caveat that body dysmorphia is real, so it is often good to get the second opinion of a coach, physician or trusted friend to make sure that you are objectively assessing what you see.
Body weight.
Your weight on the scale is a pretty good indicator of what's going on. One reason for this is that you can lose fat relatively quickly compared to how fast you can gain muscle (about 4:1), so if the scale weight is going down AND you are working out, then you are probably losing fat and maybe gaining some muscle as you go. If the scale weight is going up slowly AND you are working out, AND you look more muscular and don't look less lean, then you are probably gaining muscle with minimal fat gain. Are you gaining weight fast and looking less defined? Then you are probably in a large calorie surplus and are gaining significant body fat along with any muscle, which may actually be your goal in specific contexts.
Skin Folders
Skin folds are another really good measure, like body circumference, for assessing body fat changes. Skin folds measure the amount of subcutaneous fat (under the skin but outside of the body cavity/organs) in a certain area. For accurate measurements, it is best to get someone who is trained as you want to consistently measure at the same sites and with the same technique and amount of pressure. Don't bother converting these to BF% because that adds in errors, just sum up the different measurements. If the sum of your measurements across four sites went from 200mm to 140mm, then you have almost definitely lost subcutaneous fat. You can also use a “pinch” test to get a rough gauge. If you pinch the skin around your waistband and there is less between your fingers than there used to be, then you have probably lost fat there.
The Power of Many
The best way to use the above assessments is as points for or against a result. If the majority of them are pointing in the same direction, then the suggested outcome is probably what is happening. For example, if your scale weight is down, your skin folds have decreased, but you can't really see a difference in your progress pictures, then you have probably lost body fat but just not enough to make a visual difference yet or not in areas that are very apparent. If you go from having a reasonable amount of belly fat to a bit less belly fat but still not enough to see your abs, then it can be hard to see a difference, even if there has been a significant and measurable change.
In summary, don't bother with BIA body composition assessments (or any other type of body composition assessment for that matter, DEXA, Bod Pod etc) because the size of the error for estimating changes in an INDIVIDUAL is too large to base decisions on. If you can't base decisions on it, then it is just an expensive number on a piece of paper. If you would like to read more about BIA and other methods of accessing body composition there is a brilliant in-depth series of articles here by James Krieger.
If you would like help using and interpreting the assessments that I did recommend and how to actually set up your training and eating to make those changes, then contact me below, and I can help you figure out what your next steps should be.
Want a free Body Weight Tracker that will graph and work out the weekly averages for you? Download that here.
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