The 2025 Lancet Commission’s “clinical obesity” definition incorporates measures of adiposity and organ dysfunction, contrasting with traditional BMI-only diagnosis.
Applying this definition in 56 low- and middle-income countries (LMICs) resulted in over 50% reductions in obesity prevalence in some regions.
The new framework improves disease specificity but raises questions about missed opportunities for primary prevention and surveillance challenges.
Global implementation faces barriers related to data availability and potential undercounts in resource-limited settings.
Background
Obesity, a leading risk factor for non-communicable diseases (NCDs) such as type 2 diabetes, cardiovascular disease, and certain cancers, is typically defined by body mass index (BMI). However, BMI alone does not account for body fat distribution or obesity-related organ dysfunction, potentially misclassifying risk and disease state. In January 2025, the Lancet Commission advanced a new definition—”clinical obesity”—requiring evidence of excess adiposity (via waist circumference or waist-to-hip ratio) and clinical assessment for organ dysfunction or functional limitations. This paradigm aims to align obesity diagnosis with actual health risks and disease burden.
Study Overview and Methodological Design
Carrillo-Larco et al. conducted a cross-sectional analysis using data from the WHO’s STEPS survey, encompassing 142,250 adults across 56 countries distributed over six global regions. The study compared traditional BMI-only obesity (BMI ≥30 kg/m²) to a modified clinical obesity definition: BMI ≥30 kg/m² with elevated waist circumference and at least one marker of organ dysfunction (e.g., hypertension, hyperglycemia, hypercholesterolemia). Due to data constraints typical in LMICs, the full spectrum of organ dysfunctions from the Lancet definition was not captured. Prevalence rates were age-standardized, and both absolute and relative changes between definitions were calculated.
Key Findings
The prevalence of clinical obesity was consistently lower than BMI-only obesity across all surveyed regions. Notably:
Men: Clinical obesity prevalence ranged from <1% (Timor-Leste, Rwanda, Malawi, Ethiopia, Eritrea, Cambodia) to 29% (American Samoa, Cook Islands, Tokelau).
Women: Prevalence ranged from ≤1% (Vietnam, Timor-Leste, Rwanda, Ethiopia, Eritrea, Cambodia) to 28% (American Samoa, Tuvalu).
In some countries, such as Malawi, the relative reduction in prevalence exceeded 65% (BMI-only obesity 0.7% vs. clinical obesity 0.2%).
Western Pacific nations (e.g., Nauru, American Samoa) experienced both large relative and absolute reductions, with prevalence nearly halved in some populations.
These shifts reflect the exclusion of individuals with high BMI but lacking evidence of organ dysfunction or functional impairment from the “clinical obesity” category.
Mechanistic Insights and Pathophysiological Context
BMI is an indirect proxy for adiposity and not a direct measure of metabolic risk. Central adiposity (as measured by waist circumference or waist-to-hip ratio) correlates more closely with visceral fat, which is metabolically active and strongly associated with insulin resistance, dyslipidemia, and vascular dysfunction. The clinical obesity definition’s requirement for organ dysfunction or limitations intends to capture those who have transitioned from risk factor (preclinical) to disease state (clinical), harmonizing diagnostic criteria with downstream health consequences.
Clinical Implications
For clinicians, the new definition offers a more nuanced framework for identifying patients at imminent risk of morbidity and mortality from obesity-related complications. This could refine eligibility for pharmacotherapy, bariatric surgery, or intensive lifestyle interventions, focusing resources on those with demonstrable end-organ impact. However, the reclassification of many individuals from the “diseased” to “at-risk” category (preclinical obesity) may inadvertently deprioritize primary prevention efforts or access to early intervention—paralleling longstanding debates in hypertension and prediabetes management.
Limitations and Controversies
The study’s reliance on a subset of the full clinical obesity criteria (due to data scarcity in LMICs) may underestimate true prevalence. The definition’s complexity also presents practical challenges for population-level surveillance and may exacerbate health inequities where measurement tools and biochemical assessment are unavailable. Critics argue that the binary distinction between preclinical and clinical obesity could delay preventive care or stigmatize those with risk but not yet disease. The Lancet Commission counters that preclinical obesity should be managed akin to other risk factors, not dismissed.
Expert Commentary or Guideline Positioning
Over 75 medical organizations have endorsed the new definition, reflecting a shift toward precision medicine in obesity management. However, Carrillo-Larco and colleagues warn that “there is little to no opportunity for primary prevention of clinical obesity, as its definition already includes a cardiometabolic condition that most likely warrants secondary prevention or treatment.” The debate mirrors shifts in cardiovascular and metabolic disease frameworks, where risk stratification is increasingly nuanced but may complicate public health messaging.
Conclusion
The transition to a clinical obesity definition represents a significant advance in aligning diagnostic criteria with health outcomes but has profound implications for global epidemiological surveillance, clinical care, and policy. While the new framework increases disease specificity, it also highlights critical gaps in data infrastructure, especially in LMICs, and raises ethical and practical questions about prevention and access. Future research should focus on validating the definition’s predictive value for hard outcomes and developing pragmatic tools for implementation in diverse healthcare settings.
References
Rubino F, Cummings DE, Eckel RH, et al. Definition and diagnostic criteria of clinical obesity. Lancet Diabetes Endocrinol. 2025 Mar;13(3):221-262. doi: 10.1016/S2213-8587(24)00316-4IF: 41.8 Q1 B1. Epub 2025 Jan 14.Carrillo-Larco RM, et al. Prevalence of clinical obesity according to a new definition: a cross-sectional analysis of population-based surveys in 56 countries. PLOS Glob Public Health. 2025 Jul 24.
