Obesity has traditionally been considered a risk factor for various diseases. However, it is increasingly recognized as a disease by medical societies and governments. The 2020 Canadian Adult Obesity Clinical Practice Guidelines stated, “Obesity is a prevalent, complex, progressive, and relapsing chronic disease, characterized by abnormal or excessive body fat (adiposity) that impairs health.” Similarly, in 2024, the World Health Organization (WHO) defined obesity as “a chronic, complex disease characterized by excessive fat deposits that can impair health.”

The shift from viewing obesity as a risk factor to recognizing it as a disease remains controversial, impacting public health policies and treatment strategies for individuals with obesity. The primary point of contention lies in the WHO’s body mass index (BMI) thresholds, which were initially designed to predict disease risk, rather than to diagnose disease in individuals. Some people with a BMI of 30 or higher—traditionally used to define obesity—may not experience organ dysfunction or physical limitations. Conversely, others with a BMI below 30 may develop obesity-related impairments and complications.

The Lancet Diabetes & Endocrinology Commission

The Lancet Diabetes & Endocrinology Commission recently addressed these controversies by proposing refined definitions for “clinical obesity.” Their goal was to provide objective criteria for diagnosing clinical obesity to improve clinical decision-making, prioritize treatments, and guide public health strategies. This effort involved 58 experts from diverse medical disciplines and individuals with personal experience of obesity to incorporate patient perspectives.

Definitions and Recommendations by the Lancet Commission

Obesity is characterized by excess adiposity, determined through one of the following criteria:

• BMI ≥ 30 plus an elevated anthropometric measure (e.g., waist circumference ≥ 102 cm for men and ≥ 88 cm for women; waist-to-hip ratio > 0.90 for men and > 0.85 for women; waist-to-height ratio > 0.5).*
• Two elevated anthropometric measures regardless of BMI.
• Direct body fat measurement (e.g., DEXA scan).
• BMI ≥ 40.

*Values are for Caucasian populations; criteria for other ethnic groups may vary. Research is warranted to identify more precise and reliable cutoffs.

Preclinical obesity is a state of excess adiposity in which the function of other tissues and organs remains intact but is associated with an increased risk of developing clinical obesity and other chronic noncommunicable diseases, such as type 2 diabetes, cardiovascular diseases, certain cancers, and mental health disorders.

Clinical obesity is a chronic disease due to obesity alone and characterized by signs and symptoms of ongoing organ dysfunction and/or reduced ability to conduct daily activities (e.g., bathing, dressing, using the toilet, maintaining continence, or eating). People living with clinical obesity have reduced tissue or organ function due to obesity, such as (1) breathlessness caused by the effects of obesity on the heart or lungs, (2) a cluster of metabolic abnormalities, (3) knee or hip pain with joint stiffness and reduced range of motion, and (4) dysfunction of other organs including kidneys, upper airways, and the nervous, urinary, and reproductive systems.

The Lancet Commission recommends that individuals with clinical obesity have timely access to evidence-based treatments aimed at improving—or, when possible, resolving—the clinical manifestations of the condition while preventing progressive organ damage. The focus should extend beyond surrogate measures like weight loss to encompass broader health outcomes. Managing obesity-related conditions, such as cardiovascular, metabolic, or musculoskeletal disorders, may require varying levels of treatment intensity and degrees of weight reduction.

For individuals with preclinical obesity, management should prioritize risk reduction and the prevention of progression to clinical obesity or related diseases. This includes health counseling to support weight maintenance or loss, continuous monitoring, and targeted interventions for those at higher risk of developing obesity-related conditions.

Criticism and Concerns

The European Association for the Study of Obesity (EASO) has expressed the following main concerns on the new definitions proposed by the Lancet Commission:

1. Potential delays in treatment: Classifying preclinical obesity as a state of preserved health might postpone necessary interventions, leading to worse long-term health outcomes.
2. Diagnostic challenges: The lack of a clinically validated definition for “excess adiposity” could make it challenging to diagnose obesity accurately.
3. Impact on access to care: The new classification system could unintentionally create barriers to treatment, complicate insurance coverage, and increase stigma.

Implications for the Treatment of People With Eating Disorders and Higher Weight

Despite ongoing debates regarding the definitions of clinical and preclinical obesity, The Lancet Diabetes & Endocrinology Commission’s classifications have potentially valuable clinical implications for individuals with eating disorders and higher weight.

People with eating disorders and higher weight face a triple burden of stigma—related to obesity, eating disorders, and mental health conditions. Recognizing clinical obesity as a disease may help reduce some of this stigma, particularly concerning body weight.

Given the frequent overlap between eating disorders and higher weight, a well-structured approach to treating obesity and eating disorders should prioritize minimizing harm, particularly the risk of triggering or exacerbating disordered eating patterns or worsening the condition of obesity.

For instance, individuals with higher weight but without obesity-related organ or tissue dysfunction or significant limitations in age-appropriate daily activities (classified as “preclinical obesity” by the Lancet Commission or in other less medicalized terms, e.g., higher weight or nonclinical obesity) should not feel undue pressure to lose weight and prematurely medicalized. Instead, efforts should focus on the treatment of their eating disorder and adopting sustainable lifestyle improvements that prevent the progression to clinical obesity while reducing the likelihood of reinforcing restrictive eating habits or body dissatisfaction.

Conversely, individuals with both an eating disorder and clinical obesity require a nuanced, multidisciplinary, and integrated approach that moves beyond traditional, separate models of eating disorder treatment and weight-focused interventions. This necessitates collaboration among endocrinologists, psychiatrists, psychologists, dietitians, and other healthcare professionals to ensure an effective treatment that addresses the full spectrum of medical (i.e., clinical obesity) and psychological (i.e., eating disorder) needs without exacerbating either condition.

Recognizing the complexity of these conditions fosters an environment where long-term, sustainable health improvements take precedence over simplistic, weight-centric solutions. By incorporating these key considerations, healthcare systems can deliver more effective, compassionate, and comprehensive care for individuals with eating disorders and higher weight—ultimately improving both patient outcomes and quality of life.