Resting energy expenditure, weight loss, and altered body composition in HIV infection.

Failure to downregulate resting energy expenditure (REE) as an adaption to anorexia or malabsorption is often stated as the major cause of weight loss in individuals with AIDS. In a prospective study, REE was compared with weight changes in HIV-infected patients. The impact of altered body composition on REE was reassessed by critical review of the literature. Patients were 65 male HIV-infected patients, 28 with recent weight loss (WL), and 37 who were weight stable (WS); 50/65 patients had AIDS, and 29/65 had acute infections; 29 male healthy persons served as controls. Indirect calorimetry, prospective intake protocol, and bioelectrical impedance analysis were performed. Absolute REE was lower in WL patients than in controls (1459 +/- 309 versus 1711 +/- 151 kcal/d, p < 0.001) and in WS patients (1625 +/- 402 kcal/d, p < 0.05). REE/kg body cell mass (BCM) was higher in WL and WS than in controls (both p < 0.01) due to lower BCM in both patient groups (p < 0.001). REE (%Harris-Benedict) was not different among the three groups. Weight changes around the measurement were not correlated to REE (r2 = 0.0008, p = 0.82). REE was independent of diarrhea, acute infection, fever, or caloric intake. REE had a stronger correlation to body weight and to Harris-Benedict's prediction than to fat-free mass or BCM. REE explains < 1% of weight changes. Many patients can downregulate REE as an adaption to anorexia and/or malabsorption. Higher REE/kg BCM does not signify hypermetabolism at the cellular level but can be explained by the maintenance of energy-consuming visceral tissue within the BCM during BCM loss.