Whether obesity is a disease is a classification question rather than a biological one, and medical organizations answered it deliberately. The reasoning and the consequences are both worth setting out.
The question is about definition, not fact
A disease is conventionally understood as involving impairment of normal function, characteristic signs or symptoms, and resulting harm or morbidity.
Arguments for classification pointed to impaired appetite and energy regulation, measurable physiological changes, and well-established associations with other conditions.
Arguments against noted that the usual diagnostic measure describes body size rather than function, and that many people meeting the threshold have no measurable impairment.
Classification changes what the system will pay for
Coding and reimbursement follow disease classification, so designating a condition as a disease opens routes to coverage for its assessment and management.
It also creates grounds for research funding, professional training requirements and clinical guideline development that a risk factor does not automatically attract.
Those practical consequences were explicit in the debate, which is unusual, and critics argued that consequences should not determine a scientific classification.
The measurement problem did not go away
Body mass index is a ratio of weight to height that was designed for population comparison and does not distinguish muscle from fat or indicate where fat is distributed.
Two people with identical indices can differ substantially in metabolic measures, which is why classification based on that number alone attracts objection.
Clinical frameworks have moved toward staging systems that assess function, symptoms and complications alongside the size measure, producing a picture the ratio alone cannot give.
The framing affects how people are treated
Supporters argued that a disease framing shifts responsibility away from individual willpower toward physiology, potentially reducing blame in clinical encounters.
Critics countered that labeling a body size as a disease can itself be stigmatizing and may medicalize variation that carries no impairment for the individual concerned.
Evidence on which effect dominates is mixed, and the answer likely depends on how the framing is communicated in a particular consultation rather than on the classification itself.
Where the individual question is settled
Whether a particular person's weight is affecting their health is a clinical assessment involving history, laboratory results, function and symptoms, not a threshold on a chart.
That assessment, and any decision about management, belongs with a physician who can weigh the whole picture, since neither a classification decision nor a population measure answers it for an individual.