Health: How does a body mass scale work?

So, you've probably seen or heard about body fat scales that promise to measure not just your weight but also your body fat percentage. But how do these nifty gadgets actually work?

Body fat scales use a technology called bioelectrical impedance analysis, or BIA. It sounds fancy, but let’s break it down. When you step on the scale, it sends a very low, harmless electrical current through one foot, up your leg, across your pelvis, and down the other leg to the other foot. You won’t feel this current at all, so there’s no need to worry about any discomfort.

Now, here’s where the magic happens: the electrical current travels through your body, and because different tissues conduct electricity differently, the scale can measure the resistance, or impedance, it encounters. For instance, muscles and other lean tissues, which contain a lot of water, conduct electricity easily. In contrast, fat tissues, which contain less water, offer more resistance.

The scale takes this resistance data and uses it along with other information you’ve inputted, like your age, sex, height, and weight, to estimate your body fat percentage. This is possible because the impedance measurements are plugged into equations that have been developed and refined through research to predict body composition.