Weighing scale that can measure body fat via impedances

[Ephant]

Hello, how accurate are weighting scales that can measures body fat via impedances from the feet. Is the impedance of the body fat totally different from muscles, lean mass, etc. that it can be distinguished at all?

Also can it distinguish the impedances between the visceral fat and subcutaneous fat?

 

[renormalize]

Hello, how accurate are weighting scales that can measures body fat via impedances from the feet. Is the impedance of the body fat totally different from muscles, lean mass, etc. that it can be distinguished at all?

Also can it distinguish the impedances between the visceral fat and subcutaneous fat?

From the abstract to a paper from 2008: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2543039/

"...Bioelectrical impedance analysis (BIA) is a relatively simple, quick and non-invasive technique, to measure body composition. It measures body fat accurately in controlled clinical conditions but its performance in the field is inconsistent. ... We concluded that BIA measurements validated for specific ethnic groups, populations and conditions can accurately measure body fat in those populations, but not others and suggest that for large epdiemiological studies with diverse populations BIA may not be the appropriate choice for body composition measurement unless specific calibration equations are developed for different groups participating in the study."

So unless you have an AI scale that knows your ethnicity, population membership and current medical condition, your impedance body fat measurement is likely to be approximate at best.

 

[Ephant]

I bought generic china weight scale with FAT impedance measurement (no brand so not against forum rule). But examining it, there is no metal above the glass, the silver thing is inside the glass. Is it supposed to be like a capacitive screen in Ipad or is the silver thing a metal supposed to touch the feet skin in real equipment to measure the impedance?

 

[DaveE]

I bought generic china weight scale with FAT impedance measurement (no brand so not against forum rule). But examining it, there is no metal above the glass, the silver thing is inside the glass. Is it supposed to be like a capacitive screen in Ipad or is the silver thing a metal supposed to touch the feet skin in real equipment to measure the impedance?

They could have a conductive coating that you can't easily see, but I doubt it. I like your capacitive coupling hypothesis. Body fat impedance is an AC measurement; 50KHz or so.

 

[Ephant]

I tried to wear socks and stand on the scale (shown before) and still get reading of fat, muscle mass, etc. in the app. I then stand on one foot still wearing the socks, and still got a reading. Is it supposed to work even with socks? I read below it passes small electrical current up from one leg to the other:

"How do they work?

Body fat scales are easy to use. You simply step on the scale, and the tool measures both your body weight and your estimated fat percentage.

Such scales work with the help of sensors underneath your feet that use bioelectrical impedance. When you step on the scale, a small electrical current runs up through your leg and across your pelvis, measuring the amount of resistance from body fat.

Then, the sensors in the scale measure the level of resistance that the current met as it travels back through your other leg.

Depending on the type of body fat scale you have, the information can link up to your smartphone or smartwatch, as well as any fitness apps you might have.

As a rule of thumb, greater body resistance means a higher fat percentage. This is due to the fact that fat contains less water than muscle, so it’s more difficult for a current to travel through it."

 

[DaveE]

The big issue with these measurements is calibration to more accurate methods, like putting you in a tank of water. Do it the way they say to in the manual.

Unfortunately, many consumer products add features like this to get you to buy their product, or pay more for an additional feature. The consumer, on average, has no way to know if the numbers they report are actually valid. The manufacturer has more incentive to include a new feature then to prove it works well.

My heavily biased, and mostly uninformed, assessment is that this measurement is essentially only for entertainment value. Most medical types will just use BMI. Body fat isn't that important to measure well in a non-research context. Hence the lack of incentive to do it well.

 

[Fra]

Hello, how accurate are weighting scales that can measures body fat via impedances from the feet.

First of all, due to how the method works it estimates only in the path of the current. trough legs, and back to other leg.

People are different. Some people that have lots of fat have it evenly distributed. But some, commonly men, could be pretty skinny in the limbs but have a massive fat deposite in the belly.

For belly fat I suspt you MUST have a current path from feet to hands. Ie. a scale with handles.

OTOH, smartwatches, sometimes measure impdeance from arm to arm, meaning arms chest and arms. Also likely missing out belly fat.

Is the impedance of the body fat totally different from muscles, lean mass, etc. that it can be distinguished at all?

Also can it distinguish the impedances between the visceral fat and subcutaneous fat?

As with many measurement methods, one can often distinguish between "absolute accuracy" as in in between subjects, in between measuremnt occastions etc and "trending accuracy" during the course of a controlled test. I totally I agree that I think the absolute accuract of consumer devices are likely terribly bad.

As bioimpedance methods builds on assumptions of the body, which not only varies between individuals and body types, it can also vary with posture and other things can can vary within an individual. They are usually also prone to movement artifacts. But given that you always make your measurements in the same way, same posture, and similar state etc, same time of day etc, one might be able to get some "trending" data as you try to loose wight or train etc. Then the trending accuracy is more important than absolute values. For example, did i loose weight simply because I am dehydrated? it would be nice to know. But one mus still pay attention to there the current path is, as that is the area of measuement.

Some phenomena with other bioimpedancea methods. For example, you can estimate cardiac output with torso bioimpeance. It is quite good for TRENDING, on a single subject, during a single experiment. But terrible for absolut measures. But absolute measures are not always interesting.

/Fredrik