A decline in lean body mass and an accompanying increase in fat mass are known to occur during aging. The consequences of these changes in body composition may include decreased strength and physical activity, altered energy metabolism, and impaired resistance to infection. The mechanisms behind these age-related events remain unknown, but they may include changes in some of the hormonal and cytokine mediators that seem to regulate body composition. The common inflammatory condition rheumatoid arthritis could provide a useful model of these phenomena dissociated from chronological aging. This article reviews changes in neuroendocrine and immune modulators of metabolism and their consequences during aging and chronic inflammation.