Relative importance of calorie intake needed to gain weight and level of physical activity in anorexia nervosa.

We assessed whether level of physical activity of anorexia nervosa patients could influence caloric consumption needed to gain weight during hospitalization. Seventy-three percent of patients with anorexia nervosa had higher levels of motor activity than did healthy female volunteers. Anorectics required 8301 +/- 2272 kcal (mean +/- SD) to gain 1 kg body wt. Activity levels and caloric consumption needed to gain 1 kg were significantly correlated; the most active patients needed to consume more calories to gain weight. A median split of anorectic patients by level of activity showed that the group with lower activity levels gained 1 kg every 5.1 +/- 1.2 d, whereas the group with higher activity levels gained 1 kg every 7.2 +/- 1.9 d. These data suggest that the rate of weight gain can be accelerated, and the cost of hospitalization decreased, by restricting exercise in anorectics during refeeding.