Why obesity is a disease - Pathogenesis and diagnosis

Obesity is currently recognized as a complex, multifactorial chronic disease, marking a significant shift from the historical, simplistic view of mere voluntary behavior attributed solely to "excessive intake and lack of physical activity". Formal declarations by organizations such as the American Medical Association (2013) and the European Commission (2021) formally established obesity as a non-communicable, chronic, relapsing disease, acknowledging its profound health and societal implications. This recognition is crucial, as it shifts the focus away from moral judgments and weight bias toward understanding and treating the underlying physiological dysregulation. The pathogenesis of obesity is intricate and extends beyond the classical energy balance model. It involves complex neuroendocrine circuitries that regulate appetite, including homeostatic, hedonic, and emerging microbiota-driven hunger mechanisms. Adipose tissue functions as a vital endocrine organ, and its dysfunction-often involving inflammation, oxidative stress, and mitochondrial impairment-lead to ectopic lipid accumulation and chronic low-grade inflammation, driving associated metabolic comorbidities. Furthermore, the disease is shaped by multiple determinants integrated into the "exposome hypothesis," including genetic susceptibility, circadian rhythm disruptions, chronic stress, and environmental exposures such as endocrine-disrupting chemicals. Up-to-date diagnosis must reflect this complexity. Relying solely on Body Mass Index is insufficient due to its inability to differentiate between muscle and fat mass or account for crucial fat distribution. The European Association for the Study of Obesity (EASO) 2024 framework defines obesity as an adiposity-based chronic disease, emphasizing that accurate diagnosis must include both the anthropometric component (excess fat accumulation) and the clinical component, analyzing the present and potential health effects (medical, functional, and psychological impairments). Recognizing obesity as a chronic, progressive process is vital for developing targeted and effective prevention and treatment strategies.