I am using a Yunmai smart scale and an Apple watch 6 for about half a year now. I managed to reduce my weight a little and looks like my sleep improved. I definitely paying more attention to the numbers then before I had these devices.

I'm concerned sometimes we get pretty wrong measures but in average they seem to be trusty. Last week I got a low heart rate notification around 1am and I was feeling pretty sleepy that day, this happened once in half a year so I'm not very concerned.

However protein levels measured by smart scale seem to be consistently low, 16.8% (green range goes from 16 to 20%).

How can I get a better measure of protein levels?

  • 4
    Eat more protein? I think I'm missing something. I also have no idea how you measure body protein percentage.
    – C. Lange
    Jul 21 '21 at 4:00

In my experience smart scales (and in some other people's experiences) are not really trustworthy, especially in the absolute values they give, but can usually be trusted seeing trends, or how values change over time.

What's usually measured is fat and water through a small dose of electricity, not "protein" directly. This scale might be doing some strange calculations based on your weight and calculated fat to get to your "protein" (which is usually called muscle mass on DEXA scans)

If I understand your concern correctly, I'd try to go to a place where they have a well maintained DEXA scanner so you can get a better baseline and compare it with your scale.

  • my scale goes even further: there's muscle mass and protein % as separate numbers
    – Luciano
    Jul 21 '21 at 9:18
  • 1
    Wow, what does that even mean? Like your cartilages and your muscles are being counted separately? I wouldn't trust much those measures
    – user35666
    Jul 21 '21 at 9:21
  • I guess it's pure marketing. I don't even trust the body fat % (which I get regularly measured with callipers, there's already a large difference). Currently the scale says I'm at 17% protein level, whatever that means.
    – Luciano
    Jul 21 '21 at 9:38

Everything in @Paribus's answer is accurate, and most of it is even mentioned in Yunmai's own quick start guide.

How does bioelectric impedance analysis (BIA) work?

In BIA, two or more conductors are attached to a person, and a small electric current is sent through the body. The resistance between the conductors will provide a measure of body fat because the resistance to electricity varies between adipose, muscular, and skeletal tissues.

... Body composition analysis is an inexact science. Body-fat scales are rarely 100% accurate compared to professional and precise medical instruments. This is true regardless of the manufacturer or method of measurement.

It took a bit of digging to find what their "protein" measurement actually meant, but you can see it in their light2 specs.


Accuracy: 0.1%

Proteins are the main building block of the body. They are used to make muscles, tendons, organs, and skin. The percentage of protein in total body weight is around 18%.

Basically they are simply trying to estimate what percentage of your weight is from proteins. You mention that 16-20% is in the green and that you are at 16.9% which is in the green range. Even if you weren't, I wouldn't really worry about that measurement even if it was perfectly accurate. If you are worried about low protein levels anyways, eating more protein and staying fit is can't hurt.

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