Mechanisms Of Weight Loss

Several metabolic disturbances that could theoretically contribute to weight loss have been found in patients with HIV infection. For example, increased rates of resting energy expenditure (REE), averaging from 8 to more than 25% greater than controls, have been reported in stable patients across the spectrum of HIV infection (17,27-32). Even greater increases in REE may occur in patients with secondary infection (17,29). However, the presence of metabolic disturbances such as hypermetabolism cannot account fully for the magnitude of weight loss seen in many HIV-infected individuals. Instead, a growing body of evidence points to decreased energy intake as the most important contributor to HIV-associated weight loss. Grunfeld et al. (17) demonstrated that energy intake was decreased in HIV-infected patients with active secondary infections. Weight decreased by an average of 5% in four weeks during secondary infection. Weight trend correlated with energy intake but not with REE. Macallan et al. (31) measured total energy expenditure (TEE), REE, and energy intake in 27 men with HIV infection at different stages of disease. Rates of TEE were decreased in patients studied during periods of rapid weight loss, but energy intake was decreased to an even greater extent, thus accounting for the weight loss. Notably, energy intake in these patients was reduced to such an extent that it was not even sufficient to cover the cost of REE, much less that of energy required for activity. Certainly, the inability to decrease REE in the face of decreased energy intake can serve as a co-factor in accelerating weight loss, but reduced energy intake, rather than metabolic disturbances, was the primary contributor to weight loss (17,31).

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