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.  Body composition analysis is the clinical assessment of tissue and fluid compartments in the human body.  These include: fat mass; fat-free mass; body cell mass; extracellular mass; total body water; intracellular water; and extracellular water.  A normal distribution of tissue and fluid in the body is associated with immunity, high function and longevity.  An abnormal distribution of tissue and fluid in the body is associated with susceptibility, effects of disease and aging, low function, morbidity and mortality.

The purpose of body composition analysis is to assess and improve function.  For healthy persons, analysis of fat-free mass and body cell mass compartments can help maintain function, productivity, immunity, physical performance and longevity.  For persons experiencing effects of injury, disease or aging, significant disturbances in fluid and mass compartments are often critical factors determining diagnosis, treatment and client 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 on 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.

Fat mass is the total amount of stored lipids in the body and consists of the following types of fat: subcutaneous fat which is located directly beneath the skin; and visceral fat which is located deeper within the body. Fat-free mass or lean body mass, is the total amount of non-fat 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 contains all the metabolically active tissues (living cells) of the body, including muscle cells, organ cells, blood cells and immune cells.  Body cell mass also includes water inside living cells. This water is called the intracellular water and the main electrolyte of intracellular water is potassium.  Extracellular mass contains all the metabolically inactive (non-living) parts of the body such as  bone minerals and blood plasma.  It also includes the water contained outside living cells.  This water is called the extracellular water and the main electrolyte is sodium.

To perform body composition analysis, the mass and fluid compartments of the body are modeled, measurements are taken and results area analyzed.  Bioimpedance (BIA) body composition analyzers measure body composition electronically.