THE COMPONENTS OF BODY COMPOSITION

Body Composition

In order to proceed further, we need to discuss normal body composition and metabolism so that post burn alterations can be better understood. Body composition consists of two distinct components lean mass and fat mass. Lean mass typically makes up 75% body weight, being 70% water, 20% protein and 10% minerals. This component is the metabolically active part of the body. Because of its importance for survival, lean mass (fat free) is precisely regulated by metabolic pathways in order to maintain the necessary protein content for optimum body function. A decrease in lean mass reflects a loss of functioning protein as cell water is not typically lost independent of protein. The use of lean mass protein for a calorie source, is counterproductive and is limited as there are only 40,000 Kcals potentially available.

As noted, lean mass contains all the body muscle, organ structure, skin collagen and circulating proteins. Over half of the body’s protein is present in muscle.

The fat mass component is a pure energy store with no significant metabolic role except to provide fatty acids for fuel when needed for storing fat produced by excess calorie intake.

Although relative compartment size is somewhat controlled genetically absolute size changes based on environmental factors namely under or over eating relative to need.

What Happens With Loss Of Lean Body Mass? (Morbidity and Mortality)

Percent Loss of Lean Mass		Mortality
10	Impaired immunity; increased infection	10
20	Decreased healing; weakness, infection	30
30	Too weak to sit; pressure sores; pneumonia	50
40	Death, usually pneumonia	100

Because of its overall importance for all body functions, a decrease in lean mass will result in complications and an associated mortality. Clearly the objective of patient care is to minimize loss of lean mass in response to a burn.