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Stop wasting your money on Bioelectrical Impedance Analysis (BIA) scans

Mar 18, 2022

Stop wasting your money on Bioelectrical Impedance Analysis (BIA) scans

Don’t book in for a body composition scan until you read this! 


Bioelectrical Impedance Analysis (or BIA) scans are popping up in just about every gym and I’ve even seen some health professional clinics offering them as a service. 

They’re advertised as a quick and affordable way to accurately measure your body composition i.e. how much muscle, fat and bone tissue you’re made up of.

But if an athlete of mine brings me a scan to interpret, I tell them to throw it in the bin!

Here’s why….

What is a Bioelectrical Impedance Analysis (BIA) scan?

BIA stands for Bioelectrical Impedance Analysis. You see them at gyms – they're those little scales that you can either stand on or hold on to (or both) that give you a report to tell you what you're made up of. They’re really popular for the before and afters in Gym Challenges.

How does a Bioelectrical Impedance Analysis (BIA) scan work?

It sends an electrical current through the body. It uses that information to predict the amount of bone, muscle and fat you're made up of.

It’s important to note, it doesn't measure these directly. It uses formulas to interpret the scan and predict what you’re made up of.

Different types of tissues in our body have different levels of conductivity, so when the electrical signal passes through them, it spits out different results based on how easy it is for that current to move through the tissue or how hard it is.

Lean body tissue, like our bones and muscle, have a higher water and electrolyte content compared to fat, so lean tissue has a greater conductivity, which means that the electrical current passes through it easier.

The term that’s used is the electrical impedance (i.e. blocking) and the lower the reading of electrical impedance, the higher the lean body mass of that individual when we're talking about BIA scan results


A major issue with the BIA Scan

Depending on how many points of your body are touching the machine, will dictate completely different results.

If you’re using the standing scales version where you stand on the metal pads. This sends an electrical signal up one leg through the hips and straight back down the other leg. It doesn't loop through the upper body. So, if you’re bottom-heavy i.e. hold more fat on your lower half, this method give you a higher estimate of what your total fat mass.

If you’re using a machine where you only hold on to the metal handles. This sends signals in a loop from one hand, through your arm through your chest and straight back out the other hand - so it reads the top half of your body. So, if you hold more fat down the bottom it’s going to underestimate how much fat you've got, because it's only looped through the top half of your body. 

This doesn't make much sense does it when we're trying to measure our total body composition?

You may be using the BIA model where you stand on the pads and also hold on.

You get better accuracy with the four-point scans that send the signal through your whole body. 

You’ll get better data BUT there are a number of challenges with this method as a way of accurately assessing body composition.

Why you need to stop wasting your money on BIA scans

  1. How good is the machine you’re using?
    Is the machine calibrated? How long ago was it calibrated? How many people are using it? Are you using the same machine each time you’re checking your body composition? Or are they swapping new machines over constantly?

  2. BIA equipment uses a prediction equation to estimate your body composition based on the averages of a tested population (who may or may not be an athlete).

This becomes an issue if:

  • There were inaccuracies in the original body composition measure
  • The population originally tested doesn't have similar body composition to you.

So these equations may not be the right fit for you.

  1. The other major limitation of BIA scans is that you can influence the results, depending on:
  • How hydrated you are

If you are less hydrated, the current flows slower through your body, meaning there's more electrical impedance. So if you're less hydrated, then the data is going to show that you have a higher body fat percentage than you actually do.

  • How much glycogen you have stored in your muscle

When we store glycogen in our muscles, we store it with water. So, the signal goes through easier. It makes it more conductive. So, if you're glycogen depleted, maybe after a really hard training session, you've been not eating enough carbohydrate to top up your glycogen stores, or you follow a low carb high-fat diet, where there's not a lot of water in the muscle, that can trick the machine into thinking you have a higher amount of fat mass than you actually do. So, glycogen depletion means an increase in body fat percent on these scans.

Be it over-estimating lean mass, under-estimating fat mass or vice versa research suggests a significant lack of accuracy for these BIA scans. Results can vary significantly by up to 8%!

Why is accuracy of body composition assessment important?

As a Sports Dietitian, when I teach athletes what to eat for recovery or how to calculate carb-loading plans, we take their lean mass to help us calculate what their needs are. So, although it might seem quite harmless, when you're jumping on a scan quickly in the gym or at home, I'd strongly encourage you to avoid this type of scan if you really want to accurately know what you're made up of and accurately track changes over time. 

So what is the alternative to a BIA scan?

If you really want to know how much lean muscle tissue you made up off, then go and get a DEXA scan. Just be sure to select the right place to get your DEXA scan done as not all DEXA scans are created equal!

DEXA scans can also be cheated, so the other, excellent option is skin folds.

Find somebody that's good at doing skin folds so you can get accurate data.

✓ They're affordable.

✓ They're repeatable.

✓ They're not cheatable – i.e. not impacted by hydration or glycogen status.

If you haven’t already, check out my earlier podcast episode and blog on skin folds – what they are and how to ensure you’re getting them done accurately. 

I run a monthly Dietitian Approved skinfolds clinic: We have a 15-minute appointment where you get a detailed report and I'll explain to you what's going on inside your body.

Skin folds track change to the millimetre of how much subcutaneous fat you've got at the seven body sites that we measure.


To book, click HERE



When it comes to BIA scans the reality is, there is absolutely no point in measuring something if it cannot accurately track progress.

What you are doing is simply getting a number for the fun of it, a number that may or may not reflect your body composition at the time.

But remember, getting a measurement is only one very small step towards goal progression. If you’re interested in working with a Sports Dietitian, join us inside the Triathlon Nutrition Academy.


If you’re interested in joining the Triathlon Nutrition Academy, pop your name on the waitlist NOW | Join the TNA Waitlist




  1. Esco, M. R., Olson, M. S., Williford, H. N., Lizana, S. N., & Russell, A. R. (2011). The accuracy of hand-to-hand bioelectrical impedance analysis in predicting body composition in college-age female athletes. Journal of Strength and Conditioning Research, 25(4), 1040-1045. Retrieved from
  2. Comparisons of a Multi-Frequency Bioelectrical Impedance Analysis to the Dual-Energy X-Ray Absorptiometry Scan in Healthy Young Adults Depending on their Physical Activity Level
  3. Loenneke, J., Wilson, J., Wray, M., Barnes, J., Kearney, M., & Pujol, T. (2012). The Estimation of the Fat Free Mass Index in Athletes. Asian Journal of Sports Medicine, 3(3).
  4. Wang, J., Zhang, Y., Chen, H., Li, Y., Cheng, X., Xu, L., … Li, B. (2013). Comparison of Two Bioelectrical Impedance Analysis Devices With Dual Energy X-ray Absorptiometry and Magnetic Resonance Imaging in the Estimation of Body Composition. Journal of Strength and Conditioning Research, 27(1), 236–243.
  5. Position of the American Dietetic Association and the Canadian Dietetic Association: nutrition for physical fitness and athletic performance for adults
  6. Van Marken Lichtenbelt, W.D., Hartgens, F.J., Vollaard, N.B., Ebbing, S. & Kuipers, H. (2004). Body Composition Changes in Bodybuilders: A Method Comparison. Medicine & Science in Sports & Exercise, 36(3), 490-497. doi: 10.1249/01.MSS.0000117159.70295.73.

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