On World Obesity Day this year, the theme aims to change the focus from individuals to the systems that shape our health, from government and policy to healthcare systems and social determinants of health such as economic instability and food insecurity. A myriad of factors influence the rising rates of obesity worldwide1, and multiple approaches are needed to address the burden of disease.

A new commission2 published in The Lancet Diabetes & Endocrinology has now called for an overhaul of the diagnosis of obesity and a more nuanced approach, shifting focus away from the reliance on BMI as a key diagnostic criteria to symptoms and other physiological factors and biomarkers such as excess body fat and measurements of body size (waist circumference, waist-to-hip ratio and waist-to-height ratio) that offer more objective and clinically meaningful information. Two new categories of obesity were introduced — ‘preclinical obesity’ and ‘clinical obesity’ — that encompass the pathophysiology of obesity from the presence of excess body fat to alterations in organ structure and function, making the distinction between when obesity is considered a risk factor and when it can be considered a disease and causing harm. The new definition acknowledges preclinical obesity as a physical phenotype and a condition of excess body fat that is associated with variable levels of health risk and, crucially, no ongoing illness, whereas clinical obesity is a chronic disease due to obesity alone and is characterized by signs and symptoms of organ dysfunction and/or reduced ability to conduct daily activities. The hope is that these new diagnostic criteria will lead to a more accurate diagnosis that can enable more effective management for people living with obesity — risk reduction and prevention of progression for those with preclinical obesity, and improvement of signs and symptoms and organ function for those with clinical obesity.

This shift in thinking and reframing of a globally important disease has been echoed in the hepatology field. In this issue, Sookoian et al. argue that metabolic dysfunction-associated steatotic liver disease (MASLD) is a global health challenge and should be considered a non-communicable disease (NCD) and placed within the framework alongside the four current NCDs — cardiovascular disease, cancer, type 2 diabetes mellitus and chronic respiratory disease — which currently account for 74% of all deaths globally. MASLD is closely associated with type 2 diabetes mellitus, obesity and cardiometabolic health, and the revised MASLD nomenclature3 launched in 2023 acknowledged this close association with cardiometabolic factors (such as blood sugar and serum triglyceride levels) as part of the diagnostic criteria for MASLD for both adult and paediatric disease. By integrating MASLD into the NCD framework, the authors argue that comorbidities and risk factors common to the existing NCDs and MASLD (particularly behavioural, lifestyle and metabolic risk factors) can be acted on to collectively reduce the burden of these conditions. Moreover, this approach would bring MASLD to the attention of policymakers. Indeed, there should be a spotlight on MASLD: the condition currently affects around 30% of the global population, and a strong public health response is needed to address the increasing burden (for both mortality and morbidity) of MASLD and the more progressive form of the disease metabolic dysfunction-associated steatohepatitis4.

“an overhaul of the diagnosis of obesity and a more nuanced approach”

Disease definitions should evolve as our understanding of the condition improves and should always consider patients’ experiences. In developing the new commission on clinical obesity2 and the MASLD nomenclature3, experts acknowledged that stigma associated with weight and disease was an important factor that influenced their recommendations. There is no single solution to addressing these complex conditions; instead, transforming care for obesity and MASLD requires a coordinated approach that addresses multiple facets of the diseases and their effects on the human body, and the environment and systems that perpetuate these conditions and influence overall health. Every individual is unique, and effective interventions must account for this variability while also recognizing the role of policymakers, public health strategies and healthcare policies in shaping outcomes. Improved diagnosis and identification of patients is one of many steps towards improved care for obesity and MASLD. Attention is now needed on the social determinants of health, particularly the role of nutrition and food security, economic stability, and environmental factors to ensure sustainable solutions for healthier communities.