From Old to New: A Comprehensive Review of Obesity Diagnostic Criteria and Their Implications

Abstract

Obesity is a chronic, multifactorial disease that imposes significant health burdens worldwide. Although body mass index (BMI) is widely used for its simplicity and utility at the population level, it fails to capture critical clinical aspects, including body composition, fat distribution, metabolic health, and functional impairment. This review explores the limitations of current BMI-based diagnostic criteria for obesity and introduces a new definition and diagnostic framework proposed by the Commission on Clinical Obesity. The new criteria redefine obesity using clinical and biological markers and distinguish between clinical and preclinical obesity based on functional consequences and risk stratification. This approach aims to facilitate more accurate diagnoses, individualized treatment, and evidence-based health policies, while also addressing issues such as weight stigma and overdiagnosis. Further research is needed to validate this model and support its integration into clinical practice.

INTRODUCTION

Obesity is a chronic, progressive, and often relapsing condition that has reached epidemic levels globally [1]. It contributes to a wide spectrum of complications, chronic diseases, and imposes a substantial burden on health systems worldwide. Recent data indicate that overweight and obesity were responsible for an estimated 3.71 million deaths and 129 million disability-adjusted life-years in 2021 [2]. Furthermore, these conditions are among the leading global risk factors, with the most rapidly increasing impact in terms of attributable disease burden [2].

Although obesity is recognized as a disease, its diagnosis based solely on body mass index (BMI) departs from the manner in which most disease states are defined, typically by their capacity to cause illness through ongoing alterations in organ and tissue function, as experienced both objectively and subjectively. This disconnect has led to negative consequences at clinical, economic, and political levels, including obesity-related stigma and the potential for overdiagnosis.

To address these issues, the recently established Commission on Clinical Obesity has proposed a new framework based on clinical and biological criteria for defining clinical obesity [3]. This review aims to examine and critically evaluate these recommendations.

LIMITATIONS OF EXISTING DIAGNOSTIC CRITERIA

The World Health Organization defines obesity as an abnormal or excessive accumulation of body fat that poses a health risk, and has adopted BMI—calculated as weight in kilograms divided by height in meters squared—as the standard tool for its diagnosis and classification [4]. This approach is grounded in several key considerations: (1) facilitating meaningful comparisons of weight status across and within populations; (2) identifying individuals and groups at increased risk for morbidity and mortality; (3) supporting the prioritization of interventions at both individual and public health levels; and (4) providing a consistent framework for evaluating intervention effectiveness [4]. While BMI is a convenient and widely used screening tool for obesity in population-based settings, it has several limitations in individual clinical care. First, although BMI generally correlates with total body fat (with correlation coefficients typically around 0.80) [5,6] and with obesity-related outcomes such as cardiometabolic diseases, it does not distinguish between fat mass and lean mass, leading to potential misclassification [6]. For example, athletes or individuals with high muscle mass may have elevated BMIs that suggest overweight or obesity, despite low levels of body fat. Additionally, studies in Korean populations have shown that the relationship between BMI and body fat percentage varies according to age, sex, and ethnicity [6-9]. Second, BMI does not account for fat distribution—particularly visceral adiposity, which is more strongly linked to metabolic risk than subcutaneous fat [10-14]. Third, BMI cannot capture metabolic health status. Some individuals with high BMI may be metabolically healthy (with normal blood pressure, glucose, and lipid levels), while others with normal BMI may present with metabolic syndrome—a phenotype known as ‘metabolically obese normal weight’ (MONW). In a study of older Korean adults, those with the MONW phenotype exhibited higher all-cause mortality over a 10-year follow-up compared to metabolically healthy obese individuals [15]. Another analysis, using the 2009–2010 Korea National Health and Nutrition Examination Survey, reported a high prevalence of clustered cardiometabolic abnormalities in MONW individuals [16]. Finally, BMI-based anthropometric classifications do not account for comorbidities or disease risk. Moreover, changes in BMI or waist circumference do not necessarily reflect improvements in overall health or functional status. Notably, even modest weight loss of 5% to 10% has been shown to yield meaningful health benefits, despite limited changes in BMI classification [17-19].

INTRODUCTION OF THE NEW DIAGNOSTIC CRITERIA AND DIFFERENCES FROM PREVIOUS CRITERIA

Given the limitations of current diagnostic criteria for obesity, which rely predominantly on anthropometric measurements, the Commission on Clinical Obesity was established to redefine obesity in a manner that supports clinical decision-making and informs the prioritization of therapeutic interventions and public health strategies [3]. It proposed a staging system based on straightforward clinical assessments, including medical history, clinical and functional evaluation, as well as simple routine diagnostic investigations that are readily and widely available (Fig. 1) [3]. Obesity is categorized into clinical and preclinical stages based on the presence or absence of objective clinical manifestations, such as signs and symptoms of organ dysfunction or limitations in daily activities. Clinical obesity is defined as a chronic and systemic disease (Table 1), characterized by functional alterations in tissues, organs, the whole individual, or any combination thereof, resulting from excess adiposity [3]. Preclinical obesity refers to excess adiposity without dysfunction in other tissues or organs, although it is typically associated with an increased risk of progression to clinical obesity and the development of non-communicable diseases such as type 2 diabetes, cardiovascular disease, certain cancers, and mental health disorders [3]. Accordingly, although BMI has traditionally been the primary indicator for diagnosing obesity, it is now recommended to serve only as a screening tool. Diagnostic confirmation should involve more precise assessments of excess adiposity, either through direct measurements such as dual-energy Xray absorptiometry or bioelectrical impedance analysis, or, at minimum, by adding another anthropometric criterion (e.g., waist circumference, waist-to-hip ratio, or waist-to-height ratio) (Table 2) [3].

Fig. 1.

Diagnostic model of clinical obesity. BMI, body mass index.

Table 1.

Diagnostic Criteria for Clinical Obesity in Adults

Obesity-related organ dysfunction
Central nervous system	Vision loss, recurrent headaches, or both due to raised intracranial pressure
Upper airways	Apneas or hypopneas during sleep due to increased upper airways resistance
Respiratory system	Hypoventilation and/or breathlessness and/or wheezing due to reduced lung and/or diaphragmatic compliance
Cardiovascular system	• Heart failure with reduced ejection fraction (due to reduced left ventricular systolic function)
	• Chronic fatigue and lower limb edema (due to impaired diastolic function-heart failure with preserved ejection fraction)
	• Chronic or recurrent atrial fibrillation
	• Pulmonary artery hypertension
	• Recurrent deep-vein thrombosis or pulmonary embolism
	• Raised arterial blood pressure
Metabolism	The cluster of hyperglycemia, high triglyceride levels, and low HDL cholesterol levels
Liver	Metabolic dysfunction-associated steatotic liver disease with fibrosis
Renal	Microalbuminuria with reduced eGFR
Urinary system	Recurrent/chronic urinary incontinence
Reproductive system	• Anovulation, oligo-menorrhea and polycystic ovary syndrome
	• Male hypogonadism
Musculoskeletal system	Chronic, severe knee or hip pain associated with joint stiffness and reduced range of joint motion
Lymphatic system	Lower limbs lymphedema causing chronic pain and/or reduced range of motion
Limitation of daily activities
Significant, age-adjusted limitations of mobility and/or other basic activities of daily living (bathing, dressing, toileting, continence, eating)

HDL, high-density lipoprotein; eGFR, estimated glomerular filtration rate.

Table 2.

Comparison of the Traditional and New Diagnostic Criteria (Lancet Commission) for Obesity

Traditional approach	New diagnostic criteria (Lancet Commission)
Sole reliance on BMI	Diagnosis requires confirmation of excess/abnormal adiposity via:
	• Direct measurement (e.g., DEXA, bioimpedance)
	or
	• At least one additional anthropometric criterion (e.g., WC, WHR)
No clear illness definition	Clinical obesity requires:
	• Confirmed excess adiposity
	and
	• Either functional impairment of tissues/organs or significant limitations in daily living activities
Overdiagnosis risk	Differentiates between preclinical and clinical obesity, reducing risk of overdiagnosis
Obesity plus criteria for treatment	New model supports direct treatment for clinical obesity, even without comorbidities

BMI, body mass index; DEXA, dual-energy X-ray absorptiometry; WC, waist circumference; WHR, waist-to-hip ratio.

POTENTIAL IMPROVEMENTS

People with obesity often experience negative perceptions, stereotypes, and blame from others due to their body weight—phenomena commonly referred to as weight bias [20]. Weight bias is partly rooted in the misconception that individuals have complete control over their body weight, despite the fact that obesity results from a complex interplay of genetic, biological, social, economic, environmental, and behavioral factors. Weight stigma has been consistently and strongly linked to negative physical and mental health outcomes [21-24]. Moreover, the traditional definition of obesity, which focuses on body weight and relies on BMI derived from height and weight, has also been associated with weight stigma [25]. Under the BMI-based definition of obesity, which emphasizes body weight, treatment has traditionally focused on weight reduction. However, in cases of clinical obesity—defined by functional impairments of tissues or organs or significant limitations in daily living activities—the therapeutic approach shifts toward addressing the health problems caused by obesity. This shift may help to reduce weight stigma and enhance patient engagement and adherence to care.

The Commission on Clinical Obesity was established to redefine obesity in a way that informs clinical decision-making and guides the prioritization of therapeutic interventions and public health strategies [3]. The Commission distinguishes individuals with clinical obesity as appropriate candidates for active treatment, while those with preclinical obesity should undergo risk-based monitoring and receive preventive interventions [3]. This approach enables more accurate risk stratification, helping to identify patients most likely to benefit from medical or surgical treatment.

Importantly, obesity treatment should not focus solely on weight loss, but rather aim to improve functional impairments of organs or tissues, or significant limitations in daily living activities. This paradigm shift may help to avoid overdiagnosis and unnecessary treatment in individuals who do not require medical intervention (Table 2). Moreover, it has the potential to influence policy by shifting the focus away from weight-centric blame narratives and toward the management of obesity-related health complications. It may also serve as a guide for policies that encourage evidence-based coverage decisions, support more equitable access to care by focusing on clinical need rather than BMI thresholds, and enhance cost-effectiveness by prioritizing high-risk patients for intervention. Finally, it can provide a framework for policies that promote evidence-based coverage decisions, support more equitable access to care based on clinical need instead of BMI alone, and improve cost-effectiveness by targeting high-risk individuals for intervention.

POTENTIAL ISSUES WITH THE NEW DEFINITION

Although the proposed system offers potential improvements, it also presents several challenges. First, its reliance on clinical judgment to assess functional impairments and limitations in daily activities introduces diagnostic subjectivity. Without standardized and validated tools to objectively measure organ or tissue dysfunction, clinicians may differ in their interpretations of the severity or clinical relevance of these impairments, leading to inconsistencies in diagnosis and staging. Additionally, the broad range of obesity-related comorbidities, each with varying degrees of association and diagnostic ambiguity, adds further complexity. These factors make it difficult to consistently estimate obesity prevalence and hinder meaningful cross-country comparisons. Second, implementation in primary care may be challenging due to time constraints, limited training, and inadequate resources in routine clinical practice. The inherently broad and heterogeneous nature of obesity-related conditions may further complicate assessment, especially in the absence of a structured classification system that distinguishes, for example, between major and minor comorbidities. Incorporating a framework that assigns relative importance to obesity-related diseases, based on the strength of association and clinical relevance, could help improve usability. Furthermore, clearer definitions of each comorbid condition are needed to enhance diagnostic consistency. Third, the proposed staging system may fail to identify obesity-related complications that occur in individuals with lower body weights, particularly those who do not meet traditional BMI thresholds. For example, individuals with a MONW phenotype may fall within the non-obese BMI range but still possess relatively high body fat and frequently present with obesity-associated comorbidities. Nevertheless, they remain unrecognized under the current definition. Fourth, although the system is based on sound clinical rationale, its sensitivity, specificity, reliability, and practical utility remain unproven. In addition, most existing clinical trials and treatment guidelines are grounded in BMI-defined obesity rather than functional or biological criteria, which limits their applicability to this new model. To support evidence-based decision-making, further research is needed to validate the proposed framework, refine diagnostic definitions of obesity-related conditions, and develop tools that allow for consistent and scalable implementation in both clinical and public health settings.

FUTURE PERSPECTIVES

To facilitate the application and global adoption of the proposed diagnostic criteria for clinical obesity, several future directions may be considered. First, developing standardized tools and structured clinical frameworks for evaluating obesity-related functional impairments and comorbidities could be prioritized. This may include validated diagnostic instruments and clearly defined, evidence-based criteria for identifying obesity-associated conditions, along with their degree of association with excess adiposity. Implementing these measures may help reduce diagnostic subjectivity, promote consistency among clinicians, and support risk stratification, which can inform treatment priorities and enable international comparisons. Second, practical methods to implement the proposed definition in routine clinical settings, especially in resource-limited primary care, are needed. Simplified screening protocols, clinician training, and integration with electronic health record systems may facilitate this process without increasing provider workload. Third, aligning future clinical research and therapeutic guidelines with the proposed criteria is necessary. As most existing research is based on BMI-defined obesity, the clinical performance of new criteria requires further validation. Future studies should investigate health outcomes, treatment responses, and prognostic accuracy using the clinical definition to provide an evidence base for practice and policy. Finally, widespread engagement and international collaboration may be required for effective implementation. Educational efforts targeting healthcare professionals and the public can clarify the changes, enhance communication, and encourage consensus. Collaboration among clinicians, policymakers, and public health organizations will also help support the transition toward a function-based, patient-centered approach to obesity care.

CONCLUSIONS

The current BMI-based definition of obesity, while useful for population-level screening, has significant limitations in clinical practice, including its inability to capture body composition, fat distribution, and functional health status. In response, the Commission on Clinical Obesity has proposed a new definition based on clinical and biological criteria, distinguishing between clinical and preclinical obesity. This framework enables better risk stratification, reduces weight stigma, and supports more targeted interventions. However, its implementation faces challenges such as diagnostic subjectivity, limited validation, and feasibility concerns in routine care. Further research is required to standardize diagnostic tools, assess clinical utility, and facilitate the integration of this model into evidence-based practice.