Analysis of energy expenditure, endocrine function, and autonomic nervous activity in anorexia nervosa patients during refeeding

Resting energy expenditure (REE) increases in anorexia nervosa patients after refeeding; however, the associated mechanisms remain unclear. We hypothesized that changes in autonomic nervous activity are relevant to changes in REE during refeeding. The objectives of this study were (1) to confirm differences in REE during refeeding and (2) to identify the parameters associated with these differences. The subjects were 9 female inpatients with anorexia nervosa receiving cognitive-behavioral therapy. Both before and after the start of refeeding, which was defined as the first increase in food intake of 1675 kj or more per day, body composition, REE, endocrine function, R-R interval, autonomic nervous activity evaluated in terms of heart rate variability, and physical activity were measured and psychological tests completed. The differences in measurements before and after refeeding and specific associations between changes in REE and other factors were assessed. Resting energy expenditure increased significantly by 22.7% from 3190 to 3910 kj/d (P < .01) with the increase in energy intake. Fat-free mass and physical activity did not change. The increase in REE was accompanied by higher insulin-like growth factor-I, free triiodothyronine, and norepinephrine and decreases in parasympathetic activity and R-R interval. Some factors might be responsible for the increases in REE observed with refeeding. No previous study has simultaneously observed multiple variables related to energy metabolism during refeeding.