General information on body composition
The human organism consists largely of fatty tissue, bones, water and muscles, as well as other soft tissue. Since fat occupies a larger space than muscles in our bodies, the body composition together with weight is an important factor in the overall body image. For example, two people of the same size and weight can have a very different appearance if their body composition is very different.
Nowadays it is assumed that especially the amount of body fat and the ratio of this to fat-free body mass play an important role in the development of some diseases. The measurement of body composition plays an increasingly important role in clinical routine, 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 correlation between obesity and life-threatening diseases makes the determination of body composition an important instrument in everyday medical life.
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 contains only one large one: the weight.
This is determined with the help of a personal scale, whereby further analyses regarding the composition are not possible. The 2-compartment model, where in principle a distinction is made between fat and fat-free mass, including lean mass. Within the fat-free mass, this model can also differentiate between minerals, proteins and water.
The 3-compartment model represents a division of the lean mass into two different components. In the model, this lean mass (FFM) is divided into body cell mass (BCM) and extracellular mass (ECM). The BCM includes muscles, internal organs and the cells of the immune system and functions as metabolically active tissue and protein storage of the body, while the ECM refers to connective tissue, bones, extracellular water (ECW) and plasma.
Consequently, the 3-compartment model can be extended by two additional 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 represents a part of the extracellular mass. Together, these two quantities make up total body water, also known as TBW (total body water). The models differ in the accuracy of the description and subdivision of the composition of the substances that occur in the body, but none of the models is incorrect. Further subdivisions could be made, but further subdivisions usually do not make clinical sense.
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