Obesity is a worldwide main health concern, with a high treatment failure. This chapter focuses on the definition of obesity, based on excessive fat accumulation and thus underscores the importance of body composition, and the clinical tools currently used to diagnose it, mainly body mass index that is only a proxy measure of body composition. It also highlights the importance of the personal commitment to comply to a healthy diet and physical activity recommendations since surgery is most effective when accompanied by lifestyle modifications. Additionally, it addresses the description of types of patients who could benefit most from surgical management of excessive body fat percentage and metabolic derangements, as well as on the indications for surgery that are currently valid.
Keywords: Adiposity; Bariatric surgery; Body composition; Candidate; Comorbidities; Detailed phenotyping; Fat-free mass; Indications; Metabolic surgery.