How do scales read body fat?

Scales that measure body fat typically use a method called bioelectrical impedance analysis (BIA). Here's how it generally works:

1.Electrical current transmission: When you step on the scale, a very weak, safe electrical current is sent through your body. The current usually travels from the electrodes on the feet (in the case of a regular body fat scale) through the lower body tissues. Some more advanced scales may also have hand electrodes to allow the current to pass through a larger portion of the body, including the upper body.

2.Resistance measurement: Different types of body tissues have different electrical conductivity properties. Fatty tissue has a higher resistance to the flow of the electrical current compared to lean tissues such as muscle, bone, and water. Muscle and body fluids, which contain electrolytes, are good conductors of electricity, while fat is a poor conductor.

3.Calculation of body fat percentage: The scale measures the impedance (resistance) of the electrical current as it passes through your body. Using algorithms that take into account factors such as your age, gender, height, and weight (which you often input into the scale or its associated app), the device then estimates the proportion of body fat. The assumption is that based on the measured impedance and the known relationships between tissue types and electrical conductivity, it can calculate how much of your body mass is composed of fat.

It's important to note that while body fat scales can provide a convenient estimate, they are not as accurate as some other methods like dual-energy X-ray absorptiometry (DXA) scans or hydrostatic weighing. Factors such as hydration levels (dehydration can increase the apparent body fat percentage, while being well-hydrated can lower it), the time of day, recent exercise, and menstrual cycle in women can all affect the readings from these scales.