The pathophysiology of wasting in the elderly.

Aging is associated with changes in body composition and energy and protein metabolism that are due both to the direct effects of aging and to the effect of age-related diseases. We have recently differentiated these changes under three categories: wasting, cachexia, and sarcopenia. We have defined wasting as unintentional loss of weight, including both fat and fat-free compartments. Experience in the HIV epidemic suggests that wasting is driven largely by inadequate dietary intake. Cachexia, on the other hand, refers to loss of fat-free mass, and especially body cell mass, but with little or no weight loss. The metabolic hallmarks of cachexia are hypermetabolism and hypercatabolism, driven by inflammatory cytokine-mediated acute phase responses. Finally, sarcopenia refers to loss of muscle mass specifically, and seems to be an intrinsic age-related condition. In the elderly, wasting as defined here is at the extreme end of the spectrum, but generally develops in the setting of pre-existing sarcopenia and cachexia. The challenges before us now are to better define these conditions, establish guidelines for their recognition, and develop better methods for intervening when appropriate.