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