Energy expenditure economy induced by decrease in lean body mass in anorexia nervosa.

In anorexia nervosa, the low energy input associated with the classic overactivity during the malnourished state needs a sparing of energy expended at rest and also during physical activity. Therefore, we measured energy expenditure, both at rest and during moderate bicycling exercise (30W, 6 min), in 11 adult anorectic patients (weight 35.15 +/- 4.30 kg, mean +/- s.d.) at the beginning of their treatment and again after a mean weight gain of about 8.4 kg. During the malnourished state, the resting energy expenditure (REE) was lower than that predicted according to Harris and Benedict (P less than 0.001). Although it was significantly increased after weight gain (P less than 0.05), the REE per kg of lean body mass remained unchanged after repletion. The total oxygen consumption related to exercise remained unchanged after refeeding (2114 +/- 487 ml/15 min, basal vs 2168 +/- 394 ml/15 min, repletion) (n.s.). Thus in anorexia nervosa, weight loss and malnutrition did not induce economy either in energy expended at rest per unit of lean body mass nor in the energy expended in moderate cycling activity.