Body composition analysis is the clinical assessment of tissue and fluid distribution in the human body. The body is modeled as a series of tissue and fluid compartments. Fat Mass (FM) is the total amount of stored lipids in the body and consists of the following types of fat:
Subcutaneous Fat is located directly beneath the skin. Subcutaneous fat serves as an energy reserve and as insulation against outside cold.
Visceral Fat is located deeper within the body. Visceral fat serves as an energy reserve and as a cushion between organs.
Fat-Free Mass (FFM), also called Lean Body Mass (LBM), is the total amount of nonfat (lean) parts of the body. It consists of approximately 73% water, 20% protein, 6% mineral, and 1% ash.
Fat-free mass is further divided into body cell mass and extracellular mass:
Body Cell Mass (BCM) contains all the metabolically active tissues (living cells) of the body, including muscle cells, organ cells, blood cells, and immune cells. BCM includes the "living" portion of fat cells, but not the stored fat lipids. BCM also includes water inside living cells. This water is called Intracellular Water (ICW). The main electrolyte of intracellular water is potassium.
Extracellular Mass (ECM) contains all the metabolically inactive (non-living) parts of the body, such as bone minerals and blood plasma. ECM includes water contained outside living cells. This water is called Extracellular Water (ECW). The main electrolyte of extracellular water is sodium. The figure above provides a graphical representation of the relationship of mass and water distribution.
Research has shown that body composition correlates directly to a continuum of health, ranging from mortality and morbidity to immunity, longevity, high function, and athletic performance.
The purpose of body composition analysis is to assess and improve function. For healthy patients, analysis of fat-free mass and body cell mass compartments can help maintain function, productivity, immunity, physical performance, and longevity.
For patients experiencing effects of injury, disease, or aging, significant disturbances in fluid and mass compartments are often critical factors determining diagnosis, treatment, and patient outcome. Exercise, modified diet, nutritional support, and drug therapies can be prescribed to elevate levels of fat-free mass and body cell mass.
The effects of disturbances in mass and fluid compartments are largely independent of specific disease processes. Early detection of changes in body composition due to chronic disease can lead to early intervention. For example, overt symptoms of HIV/AIDS wasting often lag changes in body composition by several months.
