Obesities: Controversies in Diagnosis and Classification

Body mass index (BMI) is still the most widely used indicator of obesity, and it is widely accepted as a strong predictor of excess weight-related mortality. However, in several clinical settings, in patients with many different diseases, an inverse association between BMI and mortality has been reported: hemodialysis, cardiovascular diseases, hypertension, stroke, diabetes, chronic obstructive pulmonary disease, surgery, etc. This counterintuitive phenomenon is now called obesity-survival paradox (OP). In recent years, two other contiguous concepts have received a great deal of attention. The expression metabolically healthy obesity (MHO) indicates a phenotype with BMI <30 but not having any metabolic syndrome component and having a homeostasis model assessment of insulin resistance, (HOMA) <2.5. On the other hand, metabolically obese normal-weight (MONW) individuals are normal-weight persons who display obesity-related phenotypic characteristics. Crucial areas of research are the interactions that link MHO, MONW, and OP with body composition, fat distribution, aging, and cardiorespiratory fitness. All these phenomena are very controversial and appear as a consequence of the frail current diagnostic definition of obesity based only on BMI. A new commonly established classification of obesities based on specific variables is needed.