What are the current definitions and treatment approaches for obesity?

New Obesity Definitions

Obesity is now defined as a chronic, systemic disease characterized by excess adiposity that causes alterations in tissue and organ function, moving beyond simple BMI thresholds to incorporate functional impairment and body composition measures. 1

Evolution from BMI-Centric to Functional Definitions

The traditional definition of obesity as BMI ≥30 kg/m² remains the WHO standard for epidemiological purposes, but this approach is increasingly recognized as inadequate for individual clinical assessment. 1, 2 The most significant paradigm shift is the 2025 Lancet Commission's distinction between "preclinical obesity" (excess adiposity with preserved organ function) and "clinical obesity" (excess adiposity causing measurable organ or tissue dysfunction). 1

Clinical Obesity Diagnostic Criteria

Clinical obesity requires confirmation of excess adiposity PLUS one of the following: 1

• Evidence of reduced organ or tissue function due to obesity (abnormal signs, symptoms, or diagnostic tests showing dysfunction in one or more organ systems)
• Substantial, age-adjusted limitations of daily activities specifically attributable to obesity affecting mobility or basic activities of daily living (bathing, dressing, toileting, continence, eating)

Confirming Excess Adiposity

BMI should no longer be used alone as an individual measure of health. 1 Excess adiposity must be confirmed by:

• Direct body fat measurement (when available), OR
• At least one additional anthropometric criterion beyond BMI: waist circumference, waist-to-hip ratio, or waist-to-height ratio using validated, ethnicity-specific cutoffs 1
• Exception: BMI >40 kg/m² pragmatically confirms excess adiposity without additional measurements 1

Population-Specific Definitions

South and Southeast Asian Populations

Different BMI thresholds apply due to higher disease risk at lower BMI levels: 3

• Overweight: BMI ≥23 kg/m² OR waist circumference ≥80 cm (women) or ≥90 cm (men) 3
• Exception: Brunei Darussalam uses BMI ≥25 kg/m² 3

Pediatric Severe Obesity

The American Heart Association defines severe pediatric obesity as BMI ≥120% of the 95th percentile OR absolute BMI ≥35 kg/m², whichever is lower based on age and sex. 3 This definition replaced the problematic 99th percentile cutoff due to statistical instability. 3

Recognition as Chronic Disease

The American Medical Association formally recognized obesity as a complex, chronic disease in 2013, requiring ongoing medical attention rather than episodic lifestyle counseling. 3, 4 This designation acknowledges:

• Multifactorial etiology involving genetics, metabolism, environment, and social determinants 5, 1
• Progressive nature with potential for severe end-organ damage (heart attack, stroke, renal failure) 1
• Relapsing course requiring long-term management strategies 3, 6

Clinical Implications of New Definitions

Assessment Requirements

All patients with confirmed excess adiposity require systematic evaluation for clinical obesity: 1

• Cardiovascular function (blood pressure, lipids, vascular markers) 3
• Metabolic function (glucose tolerance, insulin resistance, inflammatory markers) 3
• Respiratory function (sleep apnea symptoms) 3
• Musculoskeletal limitations affecting mobility 1
• Psychosocial functioning and quality of life 1

Treatment Prioritization

Patients with clinical obesity (functional impairment) require immediate, evidence-based treatment, not just lifestyle counseling. 1 This may include:

• Pharmacotherapy as first-line treatment for BMI ≥30 kg/m² or BMI ≥27 kg/m² with complications 6
• Bariatric surgery for severe obesity with inadequate response to other interventions 6
• Endoscopic procedures as intermediate options 6

Patients with preclinical obesity require health counseling, monitoring, and risk-appropriate interventions to prevent progression to clinical obesity. 1

Critical Pitfalls to Avoid

Do not rely on BMI alone for clinical decision-making - this both underestimates adiposity in some patients (high muscle mass) and overestimates health risk in others (metabolically healthy obesity). 1

Do not delay treatment in patients with functional impairment waiting for lifestyle modification trials - clinical obesity represents established disease requiring comprehensive treatment. 1

Do not apply Western BMI cutoffs to Asian populations - use ethnicity-specific thresholds to avoid missing patients at risk. 3

Address weight bias and stigma - these are major obstacles to effective prevention and treatment, requiring proper training for healthcare professionals. 1