Resting metabolic rate of anorexia nervosa patients during weight gain.

To determine whether changes in energy metabolism may contribute to the difficulty of weight gain observed in anorexic patients, resting metabolic rate (RMR) and neuroendocrine function were studied in 10 patients diagnosed with anorexia nervosa. RMR per kilogram lean body mass (+/- SEM) was not significantly different from that of healthy volunteers on admission (95.9 +/- 5.6 vs 103.6 +/- 3.3 kJ/kg, respectively), during early refeeding (108.6 +/- 6.9 kJ/kg), or at target weight (102.1 +/- 3.8 kJ/kg). At late refeeding RMR was significantly higher (132.1 +/- 4.9 kJ/kg, P < 0.0001). There were no significant correlations between plasma norepinephrine and thyroid hormones and RMR. The rise in RMR during refeeding is at least double that observed in other studies in which normal-weight subjects are experimentally overfed or experimentally underfed and then refed. These results suggest that the increase in RMR during refeeding is disproportionate to weight gain and this large magnitude of increase may be unique to anorexia nervosa.