Effective antiretroviral therapy, as measured by a decrease in HIV-1 RNA levels, may sustain or improve important components of body composition, perhaps through a decrease in the underlying pro-inflammatory activity and resting energy expenditure. Moderate weight gain has been reported to be associated with HAART. Meaningful increase in total body weight, however, may need to be comprised of augmentation of lean body mass (primarily muscle), since mortality in HIV and cancer wasting is associated with sizable decreases in lean body mass (LBM) and there is no evidence that increases in fat cell mass are protective. To date, there has not been any large-scale prospective evaluation of the effects of HAART on body composition. Nor has it been determined whether increasing body weight or specific components of body composition (fat or lean body mass) in persons who have lost substantive amounts of weight protects against AIDS-defining complications or prolongs survival.