I lose weight rationally and the analyser informs me that I lose muscles!

The times of checking the progress in slimming with body measurements and changes in circumferences have gone. You may say – it's a pity, because in practice, the connection of these two measurements, together with visual assessment gave the most realistic results. Nowadays, the body content analysers, which use the method of bioelectrical impedance, have become very popular. They are easy to use, simple and pleasant, but they often give surprising or even depressing values. It may turn out that during well-lead reduction, the machine shows decrease in muscle mass, not fat. In this article I will explain where such results come from.

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Can this scale be wrong? “The professional analysis of body composition”!

Body content analysis – how does it work?

There's no doubt that the measurement of body fat is the most reliable way of diagnosing overweight and obesity (compared to simple weighing or using the BMI method). There are many possible methods to use, unfortunately, majority of them cannot be done at home. Specially equipped institutions usually use so-called hydrostatic weighing or the measurement with the use of dual-energy X-ray absorptiometry (DEXA). The mentioned methods are of high precision, but they require using the equipment, which is much more expensive than an average person, or the companies which advise on diets can afford. That's why medical institutions and nutrition clinics use the less advanced method, which doesn't require a lot of experience from the staff. It is so-called analysis of bioelectrical impedance (BIA).

What is the bioelectrical impedance analysis?

The BIA method is based on the assumption that muscle and fatty tissue conduct electric current differently. During the measurement with a special machine the elecric current of low power is sent via the electrodes put on particular points on the body (bathroom scales use this method, but are far less precise). The test takes less than twenty, or up to few tens of seconds, it is painless, it doesn't require doing any special procedures, nor is it connected with the exposure to potentially harmful factors, and – what's important – it is not that expensive.

The precision of measurement with the BIA method

If the body composition measurement done with the DEXA method is perceived as quite precise (although it may also contain an error of few per cent), the tests done with the machine using bioelectrical impedance are not. Scientific data indicate that there is quite large amount of factors, which may influence the values achieved during the measurement. For example, the analysis of body composition with the use of BIA done after a meal may lead to decrease of muscle tissue even by few kilograms. The same situation may happen in case of dehydration of the body. Doing the test after physical effort may give opposite result (increase of lean body mass and underestimation of body fat). In this case, the differences may reach – attention – even more than ten kilograms. What's more, there are clear differences in precision between particular machines available on the market. Taking under consideration all the aspects mentioned above, repeating the circumstances of the measurement and whether they concern the body's conditions, become important. It occurs that during body fat reduction there may appear factors, which interrupt the measurement.

Why does the analyser show the loss of muscle mass during losing weight?

Let's be honest – during body fat reduction there may be increased muscle catabolism, which causes the loss of valuable muscle mass. But it happens very rarely that it only concerns muscle mass (although such scenario cannot be excluded, it is not so probable). Whereas, the analyser using the BIA method may present such situation. When and why does it happen?

The most frequent irregularities in body mass reduction are indicated during measurement with bioelectrical impedance in the following situations:

  • when there is significant cut on carbohydrates,

  • when there is increased presence of fat in diet,

  • when the products, such as creatine, are discontinued,

  • when duiretics are introduced.

The worst option is adding all those factors. In that case, the result of the measurement may occur appalling and cause that you follow the belief that all of your actions you take are useless.

Decrease of carbohydrate supply

In the first case, i.e. decrease of carbohydrate consumption, there is usually fast decrease of muscle glycogen. Unfortunately, such glycogen is perceived by the analyser as muscles, or at least lean body mass. Therefore, lowering its amount causes that the machine reads it as the loss of lean muscle mass. Perhaps, the differences wouldn't be so significant unless 1 g of glycogen may bind even 3g of water in cells. Just imagine – the loss of 200 – 250g of glycogen may mean the loss of even 1kg of lean body mass, sometimes within a week from starting a diet. Doing the measurement in such circumstances gives very depressing results.

Increase of fat intake

In the second case, i.e. increase of the presence of fat in diet (what sometimes happens when there is drastic cut on carbohydrates), there is even more irritating situation. The analyser may show the increase of body fat, which is connected with significant increase of intramuscular triglyceroles. The presence of these lipids is nothing to be worried about, but the analyser has some problem with it, as muscle tissue filled with lipids conducts electric impulses in a different way. And the result turns out to be disturbed again.

Discontinuation of creatine

The third circumstance concerns the mechanisms, which are similar to those occurring in case of decreasing the amount of carbohydrates. Creatine is an osmotically active substance and it binds water in muscle cells. Discontinuing its intake during reduction causes disorder of measurements during using the BIA method. This process is, obviously, more gradual than in case of carbs, but it does not mean that it depresses less. Because from week to week we can notice that lean body mass decreases (despite the fact, that lean muscle mass doesn't have to decrease).

Using diuretics

The last of the mentioned factors is also connected with the movement of water and its loss in the body. Even light diuretics, such as caffeine, dandelion, extract from parsley or nettle, may somehow influence the results achieved during the measurement with body composition analysers. You just sometimes need few doses of such product to achieve drastic result – it turns out during the test that you lost e.g. 1 kg of lean body mass within 24 hours!


Although the body composition analysers may be helpful in monitoring the progress of the work on the body, you should treat the results achieved with such method with reserve. The reason is that such machines are not so precise, as there are many factors, which may cause that the result of the measurement will be wrong.