Eli5. At home scales that measure Body fat, muscle mass, visceral fat etc etc. How do they work and how accurate are they?
In: Technology
“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.”
This is directly copied from [this site](https://www.healthline.com/health/body-fat-scale-accuracy#how-they-work) and I found it pretty accurate according to the training I have received about biometric devices when I used to work in a nursing home.
The accuracy is really dependent upon comparison to other metrics, and, from my experience, readers that provide sensors for the hands and feet tend to give a more complete reading, simply because the current travels through more of the body. As with many non-professional medical devices, by itself it is not going to give a complete picture of anything, but combined with other data, can help provide a larger, if incomplete, picture of health.
They are not accurate and differ greatly between measurements but they can help you see a trend in the measurements if you keep repeating them consistently, at the same time of day and making sure that hydration is generally equal each day.
The determination is made by measuring a current sent through the left foot and read on the right after the current has passed through the body. Water allows the current to pass more easily, fat does not and this is where some determinations are made.
Also, a 4-point device (+2 hands) will be slightly more accurate than a classic scale that only measures using the feets.
In general, you should check these parameters in the evening, when after a normal day, you are generally fully hydrated, as opposed to in the morning, when you are dehydrated and the determination will say you have a lot of fat.
Obviously, in the evening you have extra weight from eating, so the weight should be weighed in the morning, just after you get out of the bathroom.
But as I said, if you follow a diet and weigh yourself every day, you don’t necessarily care if the 25% fat percentage is correct but if after 3 months, there is a drop from 25% to 20%.
If you really need to know how accurate it is, you can take a test at a medical office that has a similar but much more accurate scale with 4 contact points plus sensors attached to the body.
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