A new definition of obesity is needed, expert analysts say

© The Lancet Diabetes & Endocrinology Commission

As obesity rates increase around the globe, the time has come for modern medicine to redefine obesity to better treat patients and guide health care policy, according to a panel of experts.

The Lancet Diabetes & Endrocrinology Commission has published its new “Definition and diagnostic criteria of clinical obesity,” a review of the science and social beliefs surrounding obesity.

Instead of just one definition or diagnosis, physicians and other clinicians should consider a two-fold description, they said.

“Obesity is a spectrum,” Commission Chair Francesco Rubino said as reported by Reuters. Rubino is a professor at King’s College London.

Clinical and preclinical

Clinical obesity “should be defined by the combination of excessive fat accumulation with specific signs and symptoms of ongoing organ dysfunction, reduced ability to conduct daily activities, or both,” the Commission report said. Patients with clinical obesity would show signs and symptoms and complications, with limitations on daily activities.

That condition should be differentiated from preclinical obesity, in which patients display excess adiposity with minor, if any, clinical manifestations. Those patients would have substantially preserved organ function, although the Commission noted those patients could have a varying, but generally increased, risk of developing clinical obesity and diseases such as Type 2 diabetes, cardiovascular disease, certain types of cancer, and some mental health disorders.

“Even though obesity exists on a biological continuum, health and illness are dichotomous conditions that can be objectively distinguished and intuitively understood by both clinicians and patients,” the Commission report said. “Distinguishing between preclinical and clinical obesity is a practical and medically meaningful approach to simplify an otherwise complex, perhaps intractable, health problem.”

In the report

The Commission report is a 42-page compendium on the science and policy around a health issue now affecting one of every eight people around the world. As of 2022, the World Health Organization estimated 2.5 billion people aged 18 years or older were overweight, and among them, 890 million were living with obesity.

The Commission noted the magnitude of the issue, and controversy around it.

“The idea of obesity as a disease is at the centre of one of the most controversial and polarising debates in modern medicine, with broad and far-reaching implications for people affected and the society as a whole,” the commissioners said in the report.

Physicians, other clinicians, researchers and patients have relied on body mass index (BMI) to measure overweight and obesity. Current measures based on BMI run the risk of underestimating and overestimating adiposity of patients. It does not supply adequate information “about health at the individual level, which undermines medically sound approaches to health care and policy,” said the report by the 58-member Commission.

BMI could suffice as a measure of health risk at the population level, for epidemiological studies, or for screening purposes. At the individual level, physicians and clinicians should rely on direct measurement of body fat, or at least one anthropometric criterion. Those could include waist circumference, waist-to-hip ratio, or waist-to-height ratio, the Commission report said.

Any patients with confirmed obesity status should be assessed for clinical obesity. Those with clinical obesity should receive timely, evidence-based treatment that aims to improve or end clinical manifestations and end-organ damage. Patients with preclinical obesity should receive counseling, appropriate monitoring over time and potentially interventions to reduce risks of clinical obesity, the Commissioners said.

Obesity debate and bias

Apart from guidelines for physicians and other clinicians, the Commission summarized the difficulties at the center of debate about obesity policy.

Recognizing obesity as a disease likely would legitimize the condition, improve access to care, and possibly reduce societal stigma, the report said, citing arguments of proponents. Weight bias remains embedded in health care, according to a 2022 meta-analysis of studies the Commission cited.

Reimbursement also is a factor. In one study, 75% of physicians felt a 10% reduction was sufficient to improve obesity-related health complications, but reimbursement was insufficient for them to treat obesity adequately.

Defining obesity as a disease also could have negative consequences, including reducing attention to individual responsibility, although the Commission said that argument may reflect societal weight bias and stigma. Among patients, obesity is highly heterogenous, and overdiagnosing it could lead to unneeded and costly use of drugs, technologies and surgeries.

“In our opinion, the question of whether obesity is a disease or merely a condition conveying risk for future ailments is ill conceived because it presumes an implausible all-or-nothing scenario, in which obesity (i.e., excess adiposity) is either always or never a disease,” said a Commission commentary on the definition. “Logic and evidence suggest that obesity can be both a risk factor and, sometimes, a disease in and of itself.”

Reframing the definition has advantages for developing a systematic approach to obesity, including prevention, clinical practice, and public health strategies, the Commission said.

“Defining obesity clinically is implicitly a call for all to pay greater attention to the effects of this illness on individuals with obesity, just as is done for other diseases that cause human suffering and premature mortality,” the commentary said.