The Lancet Diabetes and Endocrinology has sparked a global conversation with its recent commission proposing a radical redefinition of obesity. Published on 14 January 2025, the report challenges the longstanding reliance on Body Mass Index (BMI) as the primary diagnostic tool for obesity. Instead, it introduces a new framework aimed at addressing the complexities of obesity as both a health risk and a chronic disease, offering a more personalised and accurate approach to diagnosis and treatment.
The flaws of BMI as a diagnostic tool
For decades, BMI, a simple calculation of weight relative to height, has been the standard metric for obesity diagnosis worldwide. While it is easy to use and cost-effective, BMI has significant limitations. Experts argue it fails to account for important factors such as fat distribution, muscle mass, and the overall health of an individual. This has led to both overdiagnosis and underdiagnosis of obesity. For instance, athletes with high muscle mass may be wrongly classified as obese, while individuals with high body fat but normal BMI levels may go undiagnosed.
Professor Francesco Rubino of King’s College London, chair of the Lancet Commission, highlights the inadequacy of BMI, stating, “Relying solely on BMI is ineffective because it is not a direct measure of fat, nor does it provide any information about fat distribution or a person’s overall health.” This limitation has sparked calls for a more nuanced diagnostic framework that moves beyond BMI.
A new framework: Clinical and preclinical obesity
The commission proposes two new categories for diagnosing obesity: clinical obesity and preclinical obesity. Clinical obesity is defined as a chronic disease caused by excess body fat that leads to organ dysfunction, life-altering complications, or reduced ability to perform daily activities. Patients in this category often require medical interventions such as weight-loss drugs or surgery. On the other hand, preclinical obesity refers to individuals with excess body fat who do not currently exhibit organ dysfunction or significant health complications but are at increased risk of developing such issues in the future. In these cases, preventive measures such as lifestyle changes and risk monitoring are prioritised.
This distinction addresses the spectrum of obesity and acknowledges that not all individuals with excess body fat experience the condition in the same way. It also enables healthcare providers to focus resources on those who need urgent medical attention while offering preventive care to those at risk.
Beyond BMI: A holistic approach to diagnosis
The new framework incorporates additional measurements such as waist circumference, waist-to-hip ratio, and waist-to-height ratio to assess body fat and its distribution. Ideally, total body fat would be measured, but this can require time-consuming and expensive tools, such as body scans, which may not be feasible in all healthcare settings. Nevertheless, these supplementary metrics provide a clearer picture of an individual’s health risks compared to BMI alone.
The report acknowledges the practical challenges of implementing these methods. For example, healthcare professionals may need additional training to perform these measurements accurately, and standardised tools may need to be developed. However, the commission argues that the long-term benefits of accurate diagnosis and personalised care far outweigh the initial costs and logistical hurdles.
Implications for global healthcare
Obesity is a global epidemic affecting over one billion people, and its prevalence is expected to rise. In the UK alone, 26% of adults and 15% of children are classified as obese. The economic burden is staggering, with obesity-related costs to the NHS projected to increase from £6 billion annually in 2022 to £9.7 billion by 2050.
The new definitions have significant implications for healthcare systems and public health policies. Current epidemiological data, based solely on BMI, will need to be updated to reflect the spectrum of obesity. Preliminary analyses suggest that about 20% of individuals previously classified as obese may no longer meet the criteria for clinical obesity, while others with lower BMIs but significant health risks may now be included. This shift will allow for more targeted interventions, improving outcomes for individuals and reducing healthcare costs over time.
Additionally, access to treatments such as weight-loss drugs and surgery, which are often restricted by BMI thresholds, will need to be revised. This could pave the way for more equitable access to care, ensuring that individuals with clinical obesity receive the interventions they need while those with preclinical obesity are supported through preventive measures.
Shifting public perceptions and reducing stigma
The commission’s report also addresses the stigma surrounding obesity. Historically, obesity has been viewed as a lifestyle issue rather than a complex medical condition. This perception has led to blame and discrimination against individuals living with obesity, discouraging many from seeking help. By redefining obesity as a spectrum that includes both risk factors and disease states, the commission aims to foster greater understanding and compassion.
The distinction between preclinical and clinical obesity also challenges the notion that all individuals with excess body fat are unhealthy. For example, some individuals with high BMI levels may maintain normal organ function and overall health, while others with lower BMI levels may experience severe health complications. Recognising this diversity can help reduce stigma and promote a more inclusive approach to care.
Challenges and the road ahead
Despite widespread support from over 75 international medical organisations, including the Royal College of Physicians, the commission’s recommendations face practical and economic challenges. Implementing the new framework will require training healthcare providers, updating diagnostic protocols, and addressing the financial implications of more comprehensive assessments.
There is also concern about public understanding of the new definitions. Simplistic measures like BMI have long been ingrained in public health messaging, and introducing a more complex framework may cause confusion. Clear communication and education will be essential to ensure the public understands the changes and their benefits.
Experts caution that the adoption of the new framework will take time. “This is the first step in the process,” said Dr Robert Kushner, a co-author of the report. “I think it is going to begin the conversation.”
Conclusion
The Lancet Commission’s redefinition of obesity represents a paradigm shift in how the condition is understood, diagnosed, and managed. By moving beyond BMI and introducing a more nuanced framework, healthcare systems can provide better care for individuals living with obesity while addressing the global epidemic more effectively. Although the transition will require significant effort and collaboration, the potential benefits – improved health outcomes, reduced stigma, and more efficient use of healthcare resources – are immense. This new approach offers a vital opportunity to transform obesity care and improve the lives of millions worldwide.
Links
The original article from The Lancet can be obtained here: https://www.thelancet.com/journals/landia/article/PIIS2213-8587(24)00316-4/abstract
The editorial for The Lancet in which the article was published: https://www.thelancet.com/journals/landia/article/PIIS2213-8587(25)00004-X/fulltext
https://www.independent.co.uk/news/uk/academics-bmi-people-nhs-england-b2679709.html
https://www.independent.co.uk/news/health/bmi-definition-calculator-obesity-diagnosis-b2680551.html
