The principle of measuring body fat

I. Body fat detection belongs to one of the body composition analysis

It has long been applied more in the field of medical instruments. Due to the explosion of wearable devices in the last two years, some of the detection functions on traditional medical instruments have been moved to common consumer electronics such as bracelets, watches, water cups or weight scales. The more common ones are the measurement of pedometer, calorie consumption, sleep quality, heart rate, blood oxygen, body fat and other indicators.

I had introduced how to realize pedometer and sleep quality detection by using accelerometer in the series of articles on the principle of smart hardware in three minutes[1]. I have introduced the principle of heart rate detection and the design of heart rate detection module in the Daily Circuit Diagram series of articles [2].

In this article, we will introduce the principle of body fat detection and technical solution implementation on consumer electronics with body fat detection such as body fat bracelets and body fat scales.

The following figure is an introduction to the features of a certain popular body fat scale:

The first point of the figure lists numerous detectable indicators, and although there are many of them, the vast majority of them can be realized with the BIA technology as stated in the fourth point! [3]

A certain body fat scale features

BIA method is the key technology of body fat detection

Two, BIA measurement method

Traditionally, the measurement of body fat rate of the method is more complex to DEXA measurement is the main, but the time consumed and the cost of the quite uneconomical, so in the past few years there is a more convenient bio-resistance measurement (Bio- impedance analysis, referred to as BIA), which is the most convenient way to measure body fat rate. Therefore, in the past few years, a more convenient bio-impedance analysis (BIA) has been developed, which means that accurate measurements can be obtained in a very short period of time, and is suitable for use in the home and by physicians in the outpatient clinic.

The main principle of BIA is that the body is simply divided into conductive fluids, muscles, etc., as well as non-conductive adipose tissue, and the measurement is made by electrodes that emit a very small electric current through the body, and if the fat ratio is high, the measured bio-resistance is larger, and vice versa, and the BIA is a measurement of the body fat percentage through such a mechanism.

The BIA method essentially measures the body's electrical resistance

Three products that detect body fat

1. Body fat scales

There are often two electrodes on the panels of scales that detect body fat, and when the user steps on the scale with both feet, the internal BIA module measures the resistance of the subject's left foot to the right foot, and calculates the resistance of the body by combining data such as the height, weight, age, and gender of the subject, age, gender and other data to calculate body fat and other human health parameters. [4]