The main objective in the treatment of childhood obesity is to reduce the percentage of body fat mass without negatively affecting fat-free mass and, consequently, longitudinal growth. Then, it would be necessary to evaluate the changes in body compartments that may take place during the treatment of childhood obesity. In addition, there are controversial data in relation to the reduction in BMI needed to improve markers of adiposity and cardiometabolic risk factors in childhood obesity. The aim of this book is to determine the minimum change in BMI required to improve adiposity markers and cardiometabolic risk factors, and to describe the changes in several nutritional indices (body mass index, waist-to-height ratio, fat mass index and fat-free mass) in growing adolescents with obesity. enrolled in an extensive combined intervention. We hypothesized that exclusive weight loss is not imperative in order to optimize body composition and cardiometabolic risk factors in these patients.