Obesity Consensus: A Lifestyle Choice, Risk Factor, or Full-fledged Disease?

The Lancet undertook an ambitious mission by assembling a commission of 58 experts from diverse geographies and fields of medical and scientific expertise. Their goal was to define obesity not merely as a risk factor but as a “standalone” disease. Over nearly two years, the panel employed a consensus-building process to craft statements reflecting the evidence and capturing the most extensive possible agreement among its members. 

Reactions to their findings were, predictably, polarized. Supporters, including professional organizations like the American Heart Association, celebrated the effort as a landmark achievement. Critics, however, pointed to alleged biases in selecting commissioners and highlighted potential conflicts of interest—both financial and ideological. The mainstream media focused narrowly on BMI, missing the broader context, while medicine's media outlets debated the "medical flaw" of treating obesity as a risk factor rather than a disease.

The report opens with a striking acknowledgment: 

“Although the notion of disease might seem obvious, a clear definition of disease does not exist.” 

This absence of a universal definition complicates the discussion. 

Proponents of classifying obesity as a disease highlight its parallels with chronic illnesses: gradual onset, persistence, multi-organ impact, and links to health complications like diabetes, cardiovascular disease, and reduced quality of life. Even with treatment, relapses are common.

On the other hand, critics argue that labeling obesity as a disease oversimplifies its complexity. Many individuals with high BMI or excess adiposity experience no significant health issues and lead healthy lives. Furthermore, diseases often associated with obesity, such as diabetes and cancer, are distinct conditions rather than direct manifestations of obesity itself.

A Multifactorial Challenge

The commission acknowledges the complexity of obesity, stating, 

“The causes of obesity are multifactorial and still incompletely understood. Genetic, environmental, psychological, nutritional, and metabolic factors can induce alterations of the biological mechanisms that maintain normal mass, distribution, and function of adipose tissue, thus contributing to obesity.” 

This statement challenges the simplistic narrative of “calories in versus calories out,” highlighting the inadequacy of such an explanation. The fervent certainty from advocates across all sides of the obesity debate is unwarranted. 

Obesity, they assert, is more than just a risk factor; it is a condition capable of directly causing illness. The lack of a clinical identity for obesity as a disease then delays interventions and perpetuates the misconception that weight loss is purely preventative. By reframing obesity as a disease, the commission seeks to shift perspectives among patients, healthcare professionals, and policymakers.

Defining Clinical and Pre-Clinical Obesity

The commission outlined a tiered framework to define obesity. 

• Obesity: Defined broadly as excessive adiposity, with or without abnormal distribution or function of adipose tissue.
• Clinical Obesity: Characterized by systemic, chronic illness independent of other medical conditions. This includes functional changes in organs like the liver, heart, and lungs, leading to distinct symptoms or limitations in daily activities. For example, excess weight causing joint stress or mobility issues exemplifies how obesity directly impairs health.
• Pre-Clinical Obesity: A state of excess adiposity with preserved organ function, serving as a warning stage with heightened risks for non-communicable diseases like type 2 diabetes and cardiovascular disease.

The bold inclusion of daily activity limitations as a marker of clinical relevance raises subjective concerns about what should be classified as impairments. While limited mobility due to excess weight is clearly impairing, the commission’s framing also prompts debate over whether challenges like fitting into airplane seats or requiring embarrassing accommodations such as extra-large seatbelts are impairments.

Beyond BMI

The commission emphasizes moving beyond Body Mass Index (BMI) as a standalone diagnostic tool. While BMI serves as an effective screening method, an accurate diagnosis of clinical obesity requires a deeper evaluation. First, an objective measure of excess adiposity through X-ray imaging (Dual-energy X-ray absorptiometry, DEXA) or electrical impedance that characterizes the ratio of fat to muscle. Alternatively, a series of accepted anthropometric criteria, such as waist circumference, waist-to-hip ratio, or waist-to-height ratio, can be used. The goal is to move beyond mere numbers and confirm excess or abnormal adiposity through more precise methods. 

Beyond these metrics, clinicians must also evaluate obesity’s impact on the body, including reduced organ or tissue function and those aforementioned difficulties in performing daily tasks like dressing, bathing, or eating.

Managing clinical and pre-clinical obesity requires overall supervision by a qualified medical professional and comprehensive, evidence-based care. In the case of clinical obesity, care is directed to alleviate symptoms, prevent organ damage, and reduce disease progression. In contrast, pre-clinical obesity management focuses on mitigating risks and preventing the transition to more severe stages. Both involve lifestyle changes, psychological support, medications, or surgery, with treatment plans tailored to individual needs and risk-benefit assessments.

The Known Unknowns

The commission emphasizes the gaps in knowledge about obesity and the priorities for future research. They highlight that the progression from pre-clinical to clinical obesity and the specific impacts of excess adiposity on various organs remain poorly understood. While the commission advocates for a precision approach to obesity prevention and treatment, they point out that the current interventions have used lost weight rather than remission or clinical improvement, as the outcomes of interest make their treatment efficacy uncertain.

Ultimately, The Lancet’s commission takes a significant step in reframing how we understand and address obesity. By framing obesity as a disease with distinct stages and impacts, the commission seeks to reshape perceptions and guide future efforts. However, as with any ambitious initiative, questions remain. Will this new definition shift entrenched biases? Can it translate into actionable changes in policy and practice? Whether this effort leads to meaningful change or more contentious headlines remains to be seen, but one thing is certain: redefining obesity is as multifaceted as the condition itself.