Measurement methods of body composition

There are many methods to determine the body composition, which differ significantly in their procedures, accuracy and availability. The most accurate method can only be performed on the non-living body and is therefore not suitable for clinical diagnostics on living patients. All other methods have to be selected specifically according to the type of patient and the problem at hand.

A single method is not optimal for all different situations and clinical questions. In addition, when measuring on living patients, all methods have in common that they do not measure the body composition directly, but derive it via a detour from certain tissue properties. This can lead to errors which may then have an influence on the therapy during evaluation.

The method of choice for determining body composition in living human beings is currently the so-called “Bioelectrical Impedance Analysis (BIA)”. This method has been examined in many studies and publications for its accuracy and significance in relevant questions and has been found to be good. Bioelectrical impedance analysis is a diagnostic tool that enables the determination of body composition in the extended 3-compartment model.

Thus, body water, fat-free mass, lean mass, body fat, body cell mass and extracellular mass can be determined. The principle of this method is that the human body can act as an electrical resistance. Two electrodes, one on the wrist and one on the ankle, are attached, over which a small electrical current flows.

The respective voltage drop is measured, which depends on various factors.Thus, body weight, body length and the respective composition of the body tissues influence this individual drop in tension. With a known height and body weight, a detailed list of the body composition can now be made via the voltage drop. By applying special formulas, this method can also be used to draw conclusions about various diseases that are associated with cell loss.

Special clinical symptoms, for example water retention in extracellular tissue, can cause a change in the measurement results. Studies have concluded that although the method allows a good breakdown of the composition, individual calculation errors of up to 8% in the body fat percentage can occur. In bioelectrical impedance analysis, it is important that the electrodes are placed in the correct position and that the procedure is performed according to the internationally agreed standard.

Only then can the results be compared, as otherwise there may be strong fluctuations in the data. Another method for determining body composition is dual X-ray absorptiometry. Using two x-rays, which differ in their radiation energy, the body composition can be determined in three components.

Here the total body fat, bone mass and other masses can be determined. The method of dual X-ray absorptiometry is mainly used in connection with the determination of bone density, but is also used in the context of total body composition in everyday clinical practice. Another method for determining body composition is the so-called air displacement plethysmography.

Here the person to be examined is placed in a device which can be closed to the outside. The device determines the mass, and in particular the volume of the person and can thus draw conclusions about the body composition and especially the fat content. Modern medical imaging techniques also allow for a precise analysis of the body composition.

For this purpose, the use of magnetic resonance tomographs (MRT) and computer tomographs (CT) can be used. Due to the exact representation of the soft tissues of the human body, these methods can be used to calculate the composition very accurately. In the past, the so-called calipometry was often used to determine the percentage of body fat that lies under the skin.

This involves taking a fold of skin at certain points on the body and measuring its thickness using a special instrument. The mean value of these values gives a rough idea of the percentage of body fat that lies under the skin of a specific individual. The clear advantage of this method is the simplicity and speed of the procedure, as well as the fact that it is very cost-effective.

The disadvantage is that this method can only be used to determine the percentage of body fat that lies directly under the skin. Deeper lying parts of body fat cannot be determined. Also worth mentioning is the BMI or Body Mass Index, which is often used to diagnose overweight and underweight.

In clinical studies, the BMI has been linked to diseases such as type II diabetes, overweight, obesity, and eating disorders, although the link to body composition is controversial. Since the BMI does not distinguish between body fat and muscle mass, the application of the methodology may generate data that may lead to incorrect diagnoses when evaluated. Especially in children and elderly people the accuracy of the BMI decreases.

Another diagnostic tool is the measurement of the hip circumference, which is often determined in risk patients. Here, especially the body fat is determined, which accumulates in the middle of the body and is particularly harmful to the body. The disadvantage of this method is that not all body fat is determined and thus certain individuals who have a large body fat percentage and at the same time a relatively small hip circumference may have a better result than when using other methods which determine the total body fat. These topics may also be of interest to you:

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