What are body fat scales for?

Many scales can do more than just display weight. For example, they also calculate the percentage of body fat. However, the measurement has pitfalls

Do you have scales in the bathroom? It may also be able to measure body fat percentage, and you've tried that before. Perhaps you have specifically bought a body analysis scale because you want to know how much fat and muscle your organism is made up of.

Determining body composition is not only interesting for athletes and health-conscious people. The measurement can also help those who want to lose weight. If the weight remains the same despite exercise and a change in diet, for example, a body fat scale can show whether this is possibly due to newly built muscle mass.

"Conversely, it can also be seen whether you have really lost fat or just muscle mass after a diet," explains sports scientist Michael Tuttor. The latter is often the case with so-called crash diets.

How do body fat scales work?

The scales are based on the so-called bioimpedance method: a weak, imperceptible current flows through the body. Since fat conducts less well than muscle mass, there are different resistances that the device records. Together with the entries you have made for body weight, height, gender and age, the scale uses a formula to calculate the percentage of fat in the body.

Inexpensive body composition scales, however, usually have the disadvantage that the measuring electrodes are only located on the scales and therefore only come into contact with the feet. The current flows through the legs and the groin region. But the fat that is above the legs - for example on the stomach - is not recorded. "You cannot make an exact statement about the body composition with it," says Tuttor. In a test on bathroom scales, Stiftung Warentest also criticized the fact that they sometimes had large measurement errors in the body fat analysis.

Body fat scales provide more precise information if they are equipped with more electrodes. If there are sensors on the feet and hands, the fat is recorded on the legs, but also on the upper body. But here, too, inaccuracies can arise if, for example, the belly fat is insufficiently factored in.