OBESITY IS A CHRONIC DISEASE: BEYOND BMI

Abstract

For more than a century, obesity has been weighed, charted, and moralised—reduced to a ratio of height over weight squared and, too often, to a verdict of weak will. Yet since the American Medical Association recognised obesity as a disease in 2013, and with particular force since the Lancet Diabetes & Endocrinology Commission’s 2025 redefinition, medicine has begun to treat excess adiposity as what the biology always said it was: a chronic, relapsing, multifactorial illness of dysfunctional adipose tissue. This narrative review traces how obesity crossed the threshold from behaviour to disease; why body mass index (BMI), the instrument that built that threshold, is now recognised as an inadequate ruler for individuals; what adiposopathy and the genetics of energy homeostasis reveal about the condition’s mechanisms; and how the new distinction between clinical and preclinical obesity promises to end both overdiagnosis and therapeutic neglect. We examine staging systems, the treatment revolution spearheaded by incretin-based pharmacotherapy, and the unresolved tensions—stigma, medicalisation, equity, and the fate of the "obesity paradox." The evidence supports a clear thesis: obesity qualifies as a chronic disease not because a committee declared it so, but because it behaves like one—progressive, relapsing, genetically and environmentally driven, and treatable only when it is measured beyond the scale.