BMI, body composition, and the energy requirement for body weight gain in patients with anorexia nervosa

Objective: Theories abound about the energy requirements for body weight gain in anorexia nervosa (AN). We hypothesized that malnutrition status affects the energy requirements. Method: On admission, 97 AN patients were measured for body composition by dual-energy X-ray absorptiometry. The relationship between body mass index (BMI) and body composition was investigated. In addition, 21 patients who completed our treatment program were tested for energy intake and body weight. Results: The relationship between BMI and both fat-free mass and fat mass (FM) on admission was curvilinear. The weight gain per excess energy was greater in the group of patients with FM < 4 kg or BMI < 14 kg/m ² than in the group with FM ≥ 4 kg or BMI ≥ 14 kg/m2 (p = .037, p = .055, respectively). Discussion: The energy requirements for weight gain in AN patients are related to the initial FM and BMI.