The BIA scan breakdown: a valuable measure of body composition?

I can’t be the only one that’s noticed Bioelectrical Impedance Analysis (BIA) scans popping up in just about every gym 12-week challenge, or ‘get fit for summer’ promo. These scans are advertised as a ‘new’ and ‘improved’ way to accurately measure your body composition that’s not going to cost you an arm and a leg. But should you be relying on this measure when it comes to goal achievement?

It’s a no from us. Let me tell you why…


How BIA works:

Essentially, this method relies on different types of tissue in our bodies having different levels of conductivity. It sends a small current between body parts in contact with the machine (two or four points) and creates a measure of body composition depending on the response to this current. This is where we start to notice some issues, two or four points? What is that? This measure needs to be standardised if it’s going to be reliable?

BIA machines with two points (hand-to-hand, or foot-to-foot) are inferior to the four-point machines (hand-to-foot) because they won’t measure your entire body. And if you think about this logically, it makes sense. Electrical currents will always take the path of least resistance from one point to another. If you use a two-point machine, this means an entire section of your body could be missed. For example, a hand-to-hand machine, measuring an individual who holds more fat through their hips and legs, will underestimate their body fat percentage; the current will choose the path of least resistance and won’t travel through their lower body. On repeat measures, this will underestimate fat loss as you can’t show a loss of mass that was never measured in the first place. The four-point BIA set up is your better choice here.


So how is body composition measured?

Lean body tissue, like bone and muscle, has higher water and electrolyte content than fat mass. This means lean tissue has a greater conductivity, allowing the electrical current to pass through it easier. Simply put, the lower the reading of electrical impedance, the higher the lean body mass of the individual. The issue is that the water content of tissues can change depending on your hydration status. Hydration status is altered by water lost and gained throughout the day. When you eat carbohydrates, they’re broken down to the simplest form of glucose which, if not immediately used, is stored in your muscles as glycogen. The kicker is, water is wrapped up with this glycogen and stored too, increasing water content and making the muscle better at conducting electricity. So essentially the less glycogen you have stored, the MORE resistance a muscle will place on the electrical current2, and the higher the electrical impedance reading will be. Based on what I mentioned earlier, we would incorrectly interpret this lower electrical resistance reading, as higher lean body mass. In other words, any condition that depletes your glycogen stores or dehydrates you will trick the machine into reading a higher fat mass2. This means BIA can be inaccurate after a heavy training session, a big night out, or on a low carbohydrate or a ketogenic diet.

 The Truth: glycogen depletion/dehydration = BIA higher body fat percentage

So depending on your training and dietary habits in the days leading up to the test, results can vary significantly – in fact, a variance of up to 8% has been seen6. To put this into perspective, a scan on an individual who had reduced their body fat percentage by 4%, due to inaccuracy, could read an increase of 4% body fat. Not exactly a reliable measure. When we looked at the research available on the validity of BIA measures we discovered a whole host of different results for different populations: athletic and non-athletic. Some studies saw similar results to that of a DEXA (the gold standard in body composition measurement), others over-estimated lean mass and underestimated fast mass and vice versa1,2,6. All in all, this demonstrates a significant lack of accuracy.


How is the estimation made?

BIA equipment uses a prediction equation developed from a different method of body composition analysis (e.g. hydrostatic weighing/DEXA), estimating your body composition based on the averages of a tested population. This prediction can become an issue for two reasons, (1) if there were inaccuracies in the original body composition measure, or (2) if the population originally tested doesn’t have a similar body composition to you.  We could be comparing a new gym member just getting started to a high performing athlete. It’s like comparing apples and oranges…


So what are the implications of this inaccuracy?

Although it may seem quite harmless when used in a gym setting (for those looking to lose a little fat or gain a little muscle), striving to improve through an inaccurate measure is detrimental to your progress. You’re setting yourself a moving target. You’re setting goals that will change depending on your hydration status and the extent the results have varied within that 8%. 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.


What to do instead:

Our advice is instead of throwing your money into an inaccurate measure, choose a DEXA or skinfold measurement instead. If looking for an affordable, repeatable measure that isn’t impacted by hydration status then skinfolds are your best option here. There are also several other measures that you can use from home that cost nothing!

  • Progress photos
  • Clothing size
  • Girth measurements
  • Weight (although be cautious with this one depending on your goal)

If you’re interested in skinfold measurement, click the button below and book a measurement time that suits you. But remember, getting a measurement is only one very small step towards goal progression. If you’re working towards a body composition goal, book an appointment with Dietitian Approved or your local Sports Dietitian. That’s it from me, happy training!



After clicking the button above select the following:

1. Dietietic Consultation

2. Skinfolds only

3. Select an appointment time.


  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.