How do body composition monitors work?

Body composition monitors, or body fat scales as they’re sometimes called, work by measuring the level of resistance to a small electric signal that is sent from the sensors under your feet and back again.1 Don’t worry, you can’t feel a thing.2*

Some things conduct electricity (allow it to flow) better than other things. For example, metal wire lets electrical signals flow freely without resistance. Water is also known to be a good conductor. Fat, on the other hand is a poor conductor of electrical signals.

Because muscle contains high levels of water, the signal sent from the body composition sensors flows through muscle but meets resistance when it tries to travel through fat.1,2

A body composition monitor uses complex scientific calculations to estimate the level of muscle versus fat based on the level of resistance to the electrical signal.

Why are body fat monitors so useful?

Quite simply, traditional scales only provide part of the story. They provide total body weight. But if you embark on a more intensive exercise program, you will probably build muscle.

You may have heard people say, “muscle weighs more than fat.” That’s not really true, because 1 kg of muscle weighs the same as 1kg of fat – or 1kg of anything. However, muscle is denser than fat. So, if you’re carrying an extra 10kg of fat versus 10kg of muscle, your body will look and feel quite different.4 You’ll look a lot more toned with that extra muscle. The other benefit of muscle is that it boosts your metabolism, so it burns calories even when you’re relaxing on the couch.4

In other words, body composition monitors give you a better indication of muscle to fat ratio, which is important for good health.

In addition, the fat that body composition monitors measure includes visceral fat2, which is the fat surrounding internal organs – the fat you can’t see when you look in the mirror.

Too much visceral fat is thought to be closely linked to increased levels of fat in the bloodstream, which can lead to cardiovascular disease and diabetes.3

Body Mass Index (BMI) is another term you may have heard. BMI is a simple calculation that looks at your height and your weight and is used to determine whether you are in a healthy weight range for your height.5 As we saw earlier in this article, weight alone, without knowing if it’s fat or muscle, is not the ideal way to assess how healthy your body is. So, if you’d like a more complete picture of what’s going on inside, consider a body composition monitor. You can check out the BodiSure options here.

*Wearers of electronic medical devices and implants (pacemakers, electrocardiograms, etc.) are strongly advised NOT to use body composition monitors because this small current may cause a malfunction.


  1. https://www.healthline.com/health/body-fat-scale-accuracy#overview
  2. https://www.omron-healthcare.com/eu/category/digital-scales
  3. https://www.health.harvard.edu/staying-healthy/abdominal-fat-and-what-to-do-about-it
  4. https://www.healthline.com/health/does-muscle-weigh-more-than-fat#fat-vs-muscle
  5. https://www.heartfoundation.org.au/bmi-calculator



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