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What are body fat scales for?

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. Stiftung Warentest also complained in a test on bathroom scales 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.

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That falsifies the results

In addition, various factors influence the accuracy of the measurement result or falsify it. Wet feet, a full bladder, undigested muesli in the stomach, moisturizers can change the values. Another problem: "Depending on the formula with which the device calculates the body composition, the fat percentage determined can differ from the actual fat content in the organism," says expert Tuttor. This can be the case if your body proportions do not match the target figure of the formula. A study by the University of Erlangen-Nuremberg also shows that the fat mass in the body tends to be underestimated in slim people, while the scales tend to show too much fat in overweight people.

Examination at the sports doctor is more accurate

If you want to know exactly what percentage of fat and muscle there is in the body, you should consult a sports medicine specialist. It is true that sports doctors' practices often use bioimpedance analysis. However, the trained staff knows how to minimize disruptive influences and often measure with eight electrodes that they attach to different parts of the body. Important: The so-called DXA method is also used in some cases. It provides precise results, but is an X-ray examination and is therefore associated with a small amount of radiation. It is out of the question for children, adolescents and pregnant women.

In any case, let the doctor advise you in advance about which procedure he will use, what costs you will have to face and what disadvantages there may be. After the measurement, a conversation should take place to clarify what the values ​​mean for you. If you want to keep an eye on the body fat percentage in the long term, you either have to visit the sports doctor at regular intervals. Or you can buy a high-quality body composition analyzer with hand and foot electrodes, which can quickly cost several hundred euros. It is best to go to a medical supply store or sports shop.

Note: Anyone who has a pacemaker, has metal plates in their body, is pregnant or has artificial joints should clarify with the doctor beforehand whether the body fat scale can be used.

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