Involuntary weight loss is a marker of potential problems, and weight restoration is a potential solution. However, the real key diagnostic information is the status of body composition (Table 3 ). Since normal body composition for the individual of concern is not known prior to the insult, a host of normalized tables and equations, with an assumed normal value, are used. Therefore, the actual alteration of body composition caused by an insult or poor nutrition (or usually both) is not known. The complications, for example, the weakness seen in the patient, as well as the presence of a catabolic state that will lead to LBM loss, are often the best clinical markers. Of the available methods (Table 3 ), skin-fold thickness and bioelective impendence are valuable if taken sequentially over time, but some form of baseline is needed; on the other hand, nitrogen balance provides direct information as to whether the patient was catabolic or anabolic on the measurement day, and how catabolic. 22 28
Homeostasis is a concept central to the idea of stress.  In biology , most biochemical processes strive to maintain equilibrium (homeostasis), a steady state that exists more as an ideal and less as an achievable condition. Environmental factors, internal or external stimuli, continually disrupt homeostasis; an organism's present condition is a state of constant flux moving about a homeostatic point that is that organism's optimal condition for living.  Factors causing an organism's condition to diverge too far from homeostasis can be experienced as stress. A life-threatening situation such as a major physical trauma or prolonged starvation can greatly disrupt homeostasis. On the other hand, an organism's attempt at restoring conditions back to or near homeostasis, often consuming energy and natural resources, can also be interpreted as stress.