Factors related to the amount of energy required for weight gain in patients with anorexia nervosa under strict behavioral control: a study in a Japanese medical prison

Background: Weight restoration is a crucial factor in the treatment of anorexia nervosa (AN); however, there is currently no consensus on the amount of energy required to achieve weight gain in patients with AN. Methods: Forty-one patients with AN in a Japanese medical prison were included in the study. All the data were collected from their medical charts. Body weight and composition were measured using the multifrequency bioelectrical impedance device InBody 770®. Daily caloric intake was determined by subtracting the amount of calories in leftover food from that provided, and resting energy expenditure was calculated using Scalfi's formulation. These were then used to calculate daily amount of energy and energy necessary for a 1-kg weight gain (EE1). In addition, we investigated the relation between EE1 and the initial body composition values, body mass index, and AN subtype. Results: Of the 41 patients, two had EE1s that we considered outliers. Excluding these, the mean EE1 was 12,776.8 kcal/kg, with large individual differences observed (range: 6,636–22,064 kcal/kg). Significant associations were noted between EE1 and body fat mass, body fat percentage, soft lean percentage, and body water ratio. Moreover, patients with body fat mass (BFM) ≤ 3 kg (p = 0.003), body fat percentage (BFP) ≤ 8% (p = 0.008), soft lean percentage (SLP) > 85% (p = 0.011), and body water ratio (BWR) > 0.665 (p = 0.011) had higher mean EE1s. Conclusions: To gain weight, patients with AN may require a higher caloric intake than that reported in the literature for healthy women, particularly patients with less fat and more muscle. (242/350words).