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Chronic starvation secondary to anorexia nervosa is associated with an adaptive suppression of resting energy expenditure.

BACKGROUND
Chronic starvation is accompanied by a reduction in resting energy expenditure (REE). It is not clear whether this is due mainly to a reduction in body mass or also involves a significant reduction in the cellular metabolic rate of the fat-free mass (FFM).


OBJECTIVES
The main goal was to compare measured REE (REEm) with REE predicted by dual-energy X-ray absorptiometry modeling of organ-tissue mass (REEp) in malnourished patients with severe anorexia nervosa (AN) and in healthy lean control subjects. REE adjusted for FFM and fat mass was also compared between the groups.


DESIGN
This was a cross-sectional study of 30 patients with AN and 25 lean control subjects. REE was measured by indirect calorimetry. Body composition was modeled using dual-energy X-ray absorptiometry, and REE was predicted for each group based on organ-tissue mass.


RESULTS
REEm was significantly lower than REEp in subjects with AN (854 ± 41 vs 1080 ± 25 kcal/d, P < .001), but not in control subjects. In addition, REE adjusted for both FFM and fat mass was significantly lower in the subjects with AN (1031 ± 37 vs 1178 ± 32 kcal/d, P < .01). Finally, compared with the lean control subjects, both organ and skeletal muscle mass were approximately 20% smaller in subjects with AN.


CONCLUSIONS
Chronic starvation is accompanied by a significant reduction in the metabolic rate of the FFM. The organs and/or tissues accounting for this are unknown. In addition, this study suggests that protein is mobilized proportionately from organs and skeletal muscle during starvation. This too may be an adaptive response to chronic starvation.