Obesity: Classification and Diagnosis

Obesity is now recognized as a chronic or non-communicable disease; it plays a relevant pathophysiological role in the development of complications, arising as a result of complex interaction of genetic, nutritional, and metabolic factors. The physiology of weight regulation, the pathophysiology that leads to unwanted weight gain, and the maintenance of obesity have been extensively studied in recent years. The most widely used criterion for classifying obesity is the body mass index (BMI). However, according to the body fat composition and distribution, five phenotypes of obesity can be identified: (1) metabolically unhealthy obesity (MUO); (2) metabolically healthy obesity (MHO); (3) metabolically obese normal weight (MONW) phenotype; (4) normal weight obese (NWO) syndrome; (5) sarcopenic obesity. In this chapter, an extensive and detailed description of different obesity phenotypes has been offered. Furthermore, this chapter displays the diagnostic criteria of obesity according to the latest guidelines and a classification of obesity, based on primary and secondary causes (endocrine, genetic, iatrogenic, and psychological). Different definitions and classifications of obesity highlight the heterogeneity of the disease and emphasize the need of a new personalized approach for the cure of obesity.