Composition of body tissues

General information on body composition

The human organism consists largely of adipose tissue, bones, water and muscles, as well as other soft tissue. Since fat takes up more space than muscles in our bodies, body composition, together with weight, is an important parameter for the overall picture of the body. Two people of the same size and weight can look very different if their body composition is very different from one another.

Nowadays it is assumed that the amount of body fat and the ratio of this to lean body mass play an important role in the development of some diseases. The measurement of body composition is playing an increasingly important role in everyday clinical practice, although the methods of determination can vary greatly from clinic to clinic. The ever increasing number of overweight people in the population and the proven connection between obesity and life-threatening diseases make the determination of body composition an important tool in everyday medical practice.

Classification

The body composition can be divided into different groups / compartments. The respective classification is described in different body compartment models.

The 1-compartment model only contains one size: weight. This is determined with the help of personal scales, whereby further analyzes regarding the composition are not possible.

The 2-compartment model, where in principle between fat and fat-free mass, too Lean mass, is distinguished. Within the fat-free mass, this model can still distinguish between minerals, proteins and water.

The 3-compartment model shows a division of the lean mass into two different components. This fat-free mass (FFM) is converted into body cell mass (BCM =body cell mass) and extracellular mass (ECM).

The BCM includes muscles, internal organs and the cells of the immune system and functions as the metabolically active tissue and protein storage of the body, while the ECM refers to connective tissue, bones, extracellular water (ECW) and plasma.

As a result, the 3-compartment model can be expanded to include two other sizes: intracellular water (ICW), which is a component of the body cells (BCM) and extracellular water (ECW), which is located outside the cells and thus part of the represents extracellular mass. Together, both quantities result in the total body water, also TBW (total body water) called.

The models differ in the accuracy of the description and subdivision of the composition of the substances that occur in the body, whereby none of the models is wrong. Further subdivisions could be carried out, but further subdivisions generally do not make clinical sense.

Body composition measurement methods

There are many methods of determining body composition, which differ significantly from one another in terms of their method, accuracy and availability.

The most precise method can only be carried out on the non-living body and is therefore for the clinical diagnostics not suitable for living patients.

All other methods must be specifically selected depending on the type of patient and the question. A single method is not optimal for all different situations and clinical questions. When measuring on living patients, all methods also have in common that they do not measure the body composition directly, but derive it from certain tissue properties via a detour. This can lead to errors which, under certain circumstances, can influence the therapy during the evaluation.

The method of choice for determining the body composition of living people is currently the so-called "Bioelectrical Impedance Analysis (BIA)". This method has been examined in many studies and publications for its accuracy and informative value in relation to relevant questions and found to be good. The bioelectrical impedance analysis is a diagnostic tool which enables the body composition to be determined in the extended 3-compartment model. So can Body water, fat-free mass, Lean mass, body fat, Body cell mass and extracellular mass to 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 to which a small electrical current runs. The respective voltage drop is measured, which depends on various factors. Body weight, body length and the respective composition of the body tissues influence this individual voltage drop.

With a known body size and weight, a detailed list of body composition can now be made via the voltage drop. Using special formulas, this method can also be used to infer various diseases that are associated with cell loss. Special clinical symptoms, for example Water retention in extracellular tissue, can change the measurement results.

Studies have come to the result that the method allows a good breakdown of the composition, but sometimes individual calculation errors in the Body fat percentage of up to 8% arise. It is important with the bioelectrical impedance analysisthat the electrodes are attached in the right place and that the implementation is carried out according to the internationally agreed standard. Only then can the results be compared, otherwise strong fluctuations in the data can occur.

Dual X-ray absorptiometry

Another method for determining body composition is dual x-ray absorptiometry. The body composition can be determined in three components with two x-rays, which differ in their radiation energy. Total body fat, bone mass and other masses can be determined here. The method of dual X-ray absorptiometry is mainly used in connection with the determination of bone density, but is also used in everyday clinical practice in the context of total body composition.

Another method for determining body composition is the so-called Air displacement plethysmography Here, the person to be examined is placed in a device that can be locked from the outside. The device determines the mass and, in particular, the volume of the person and can thus infer the body composition and, above all, the fat percentage.

Modern medical imaging methods also enable a precise analysis of body composition. The use of Magnetic Resonance Imaging (MRI), such as Computed tomography (CT) can be used. Due to the precise representation of the soft tissues of the human body, the composition can be calculated very precisely with these methods.

In the past the so-called often came Calipometry used to determine the amount of body fat that is under the skin. Here, a fold of skin is taken at certain points on the body and its thickness is measured using a special instrument. The mean of these values ​​gives a rough overview about the percentage of body fat that is under the skin of a particular individual. The clear advantage of this method is the simplicity and speed of implementation and that the process is very inexpensive. The disadvantage is that this method can only be used to determine the percentage of body fat that is directly under the skin. Lower proportions 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. The BMI has been used in clinical studies related to diseases such as Type II diabetes, Overweight, Obesity, such as eating disorder brought, whereby the connection with the body composition is controversially discussed. Since the BMI does not differentiate between body fat and muscle mass, the application of the methodology can result in data that can lead to incorrect diagnoses when evaluated. The accuracy of the BMI decreases especially in children and the elderly.

Another diagnostic tool is that Measurement of the hip circumferencewhich is often determined in high-risk patients. In particular, the body fat is determined, which collects in the middle of the body and is particularly harmful to the body. The disadvantage here is that not the total body fat is determined and so certain people who have a large body fat percentage with a relatively small hip circumference may have a better result than when using other methods that determine the total body fat.

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Standard values

In order to be able to interpret the results from the body composition examinations, the Standard values the respective body mass must be known. These usually differ according to the Age group as well as the gender.

The entire body tissue is made up of one part in all regions water. Depending on the fluid or type of tissue, the proportion of water is more or less serious. Overall, the male, adult body consists on average about 60-65% of water. Women have a naturally higher fat percentage 50-55%. In children, the total water content is around 60-75%. Overall, the volume is distributed in a ratio of 3: 2 intracellular and extracellular Room.

The fat-free mass (FFM) is classified according to body weight. Normal values ​​are differentiated according to age and gender. Men under 30 years of age are included 80-85% in the normal range, with women in this age group at 78-80% are in the norm. Between the ages of 30 and 49, men are with 78-80% in the normal range, on the other hand women at 76-78%. Men over 49 years of age lie with 75-80% in the norm, women against it 70-75%.

In which Body fat percentage it is similar with men overall in the course of their lives between 15-22% Body fat percentage, and women agree 16-30% Body fat percentage are in the norm.

The normal range for the Body cell mass is over for men under 30 years of age 45%, in women at over 42%. At the age of 49 and over, the normal range changes and is over in men 40% and for women over 49 years of age, over 38%. The value of the body cell mass is an important value when the nutritional status as well as the general physical fitness of a person are to be assessed.