The Contested Disease: How Obesity Classification Shapes Medicine, Markets, and Patient Identity
Key Insights
The classification of obesity (search) as a disease remains deeply contested, with the AMA's 2013 vote overriding its own council's recommendation against disease status due to insufficient evidence.
The Lancet Diabetes and Endocrinology Commission proposed new diagnostic criteria moving beyond BMI alone, requiring both excess adiposity and organ dysfunction for clinical obesity (search) diagnosis.
Disease framing directs resources toward pharmacological solutions like GLP-1 drugs, potentially crowding out behavioral, psychological, and environmental approaches to obesity (search).
As global approvals of new anti-obesity (search) medicines accelerate, drugmakers have coalesced around a unified message: "Obesity is a disease." Eli Lilly launched a website asserting that obesity is not merely a risk factor for medical complications but a chronic and complex medical entity in its own right. Novo Nordisk, more circumspectly, appeals to institutional authority, noting that obesity is "recognised as a disease by the World Health Organization" and describing it as "serious, progressive and chronic."
The convergence of disease framing with the commercial success of GLP-1 receptor (search) agonists such as Wegovy and Mounjaro has reignited a longstanding debate within medicine — one that extends far beyond biology into questions of institutional power, market creation, and patient identity.
The AMA's Pivotal 2013 Decision
The American Medical Association's own deliberations illustrate the contested nature of obesity (search) classification. In its 2013 report, the AMA Council on Science and Public Health noted there was no single, clear, authoritative definition of disease, that BMI remained an imperfect clinical measure, and that it was unclear whether recognizing obesity as a disease rather than a condition, disorder, or risk factor would improve health outcomes.
The council explicitly considered the institutional consequences of disease designation: reimbursement, drug approval, prescribing behavior, insurer coverage, stigma, and the possible shift from public-health interventions toward pharmacological and surgical treatment. It concluded there was insufficient evidence to support classifying obesity (search) as a disease.
The full membership voted otherwise. As Max Moser, a research fellow in psychology at University College London, writes in STAT News, "The final overriding decision was therefore not simply a process of adjudicating biological facts, but a judgment about what classification might do."
Redefining Diagnosis: Beyond BMI
Until recently, obesity (search) has been defined solely by body mass index — those with a BMI of 30 or greater classified as having obesity. This crude calculation, as the Lancet Diabetes and Endocrinology Commission's 2024 report pointed out, does not measure fat mass, fat distribution, the type of fat a person carries, or whether excess body fat is causing harm.
"We all agree that BMI is terrible, but we can't come up with anything better," said Carel le Roux, an obesity (search) physician at University College Dublin and Commission member.
The Commission proposed defining clinical obesity (search) based on two factors: excess fat and presence of organ dysfunction. Instead of BMI alone, it suggested three assessment methods — DEXA scans, BMI with an additional body size measurement, or two body size measurements independent of BMI. The second component requires signs and symptoms related to obesity that limit day-to-day activities, such as shortness of breath, knee or hip pain, or metabolic abnormalities. The report identifies 18 specific health problems that qualify for organ dysfunction, though more than 200 complications have been linked to obesity.
Sean Wharton, a weight management physician in Toronto who co-authored Canadian obesity (search) guidelines, criticized the restriction to 18 conditions, noting it risks allowing insurers to deny coverage for those who do not meet the criteria. "If you had ADHD and it wasn't that bad yet, why wouldn't you take a medication?" Wharton said. "It's like you need it to be a shitshow before you can get medication."
Le Roux acknowledged the limitations but argued, "we have to start somewhere." When treatments remain expensive and inaccessible for most people globally, starting with those who have the most severe health problems makes sense.
The Biological Basis of Obesity (search) as Disease
Scientists have identified that a substantial proportion of obesity (search) originates in the brain, specifically in areas controlling adipocyte mass — the number of fat cells the body wants to carry. The brain regulates the mass certain organs "should" have and instructs the body to maintain that mass. Obesity appears to be a mismatch between what a healthy body's mass should be and what the brain thinks it should be.
"If we can affect that organ, we can reverse the symptoms, reverse the signs, reverse the complications, and it goes away," le Roux said. "That's why we're pretty confident we can call it a disease."
What Disease Classification Does — and What It Risks
Disease classifications, Moser argues, "do things." By naming a condition as a disease, institutions transform it from a collection of observations into a new class of object, creating new possibilities for intervention, regulation, and investment. New resources become available, new forms of expertise emerge, and new legal obligations are imposed on governments, clinicians, researchers, insurers, and patients.
Four risks accompany wholesale embrace of disease framing. The first is clinical: disease framing directs resources toward pharmacological intervention and away from behavioral, psychological, and environmental approaches, "not because those approaches are ineffective, but because they are less patentable." Last month, France's medicines regulator fined Novo Nordisk approximately $2 million and Eli Lilly $127,000 over direct-to-consumer obesity (search) awareness campaigns that regulators argued implied pharmacological treatment was the primary solution.
The second is political: when the problem is located in individual biology, the food industry, city planners, and policymakers exit the frame, along with any serious reckoning with the environments that make obesity (search) prevalent.
The third concerns risk: evidence indicates many patients who discontinue GLP-1 drugs regain much of the lost weight, creating incentives for indefinite treatment. Counterfeit markets are emerging, and the drugs are being diverted for aesthetic use. Although GLP-1 drugs have an overall favorable benefit-risk profile, gastrointestinal effects are common, discontinuation is frequent in real-world settings, and regulators continue to monitor rarer concerns including gallbladder disease, pancreatitis, aspiration risk, and psychiatric symptoms.
The fourth concerns self-conception: disease framing may reduce blame but can also recast body size as a lifelong pathology requiring surveillance and management. "The obese person once judged for lacking willpower may instead be judged for failing to comply with treatment, failing to lose enough weight, or failing to remain on medication," Moser writes.
Impact on Stigma and Clinical Care
A study published in 2020 found that physicians' perception of obesity (search) as a disease was associated with less negative weight bias. "If it's seen as a disease, it's no longer prioritized as some kind of moral failing on the part of people who live in large bodies," said Shelly Russell-Mayhew, a psychologist at the University of Calgary who led that work.
More than 100 factors may play a role in determining body weight, Russell-Mayhew noted, "yet we're focusing on the 15 percent that is probably controllable and saying you need to change your lifestyle."
For patients, understanding that "it's not all on them" can be transformative. "I've had grown men in my clinic crying," le Roux said, describing the moment patients first hear their weight is not their fault. "By you telling me it's not my fault, you give me agency."
Moser draws instructive parallels with the arrival of SSRIs in the 1990s, when depression was progressively reframed as a disorder of neurochemistry best addressed through medication. That framing entrenched a model that underemphasized psychological, social, and economic contributors — an explanation whose scientific foundations have since been seriously questioned. Today, medicine grapples with questions of efficacy, long-term use, withdrawal syndromes, and a growing de-prescribing movement, while depression remains a leading cause of disability worldwide.
"I think five years from now, we will have much better definitions because the science is moving on," le Roux said. "It's a scientific problem rather than a definition problem."