Body Composition, Resting Energy Expenditure and Physical Activity in Adolescents With Anorexia Nervosa

Body Mass Index (BMI) is currently the most widely recommended parameter for identifying underweight subjects. Among eating disorder diseases, anorexia nervosa (AN) is the one with the highest mortality rate and with relapses between 12 and 27%. To date, recovery programs allow approximately 40% of subjects to achieve recovery, 30% demonstrate improvements, and 20% remain chronically affected. These data demonstrate the importance of continuously monitoring changes in weight and body composition of these subjects. Bioelectrical impedance (BIA) is widely used to determine body composition in AN. BIA provides various parameters, such as lean mass (LM), fat mass (FM), total body water (TBW), and phase angle (PhA). Among these parameters, in addition to LM and FM, PhA has also been used to characterize underweight subjects with AN. In addition to the observed relationship between PhA and body composition in individuals with AN, PhA has also been related to the basal metabolic rate (BMR). BMR undergoes changes mainly due to loss of muscle mass and a significant reduction in BMR has been observed in AN subjects. Finally, physical activity represents a significant determinant of body composition and can help regulate BMR.

Therefore, monitoring changes in body composition (LM, FM, and PhA) and indirect indices (lean mass index and fat mass index) using BIA, together with monitoring changes in BMR and physical activity level, could provide important support for the continuous control and definition of the clinical stage of the disease in patients with AN.

The aim of this study is to determine body composition, basal metabolic rate, and level of physical activity in Anorexia Nervosa and normal weight subjects to identify the most consistent parameters to define the clinical stage of the disease in subjects with AN.