The Lancet Diabetes and Endocrinology Commission, in its 2025 report, proposed a fundamental reframing of obesity. Rather than treating a high BMI as a diagnosis in itself, the Commission distinguished between clinical obesity, in which excess body fat is accompanied by measurable organ dysfunction or limitations in daily activities, and preclinical obesity, in which excess fat has not yet caused observable harm. The distinction matters because BMI is an imperfect proxy: it overestimates adiposity in muscular individuals and underestimates it in people with central fat accumulation but normal weight. By requiring evidence of organ dysfunction, the new framework aims to identify people whose excess fat is actively damaging their health.

Applying this framework at population scale required an unprecedented collaborative effort. No single cohort had collected all the anthropometric measures, body composition data, and clinical and laboratory markers the Commission’s criteria demand. So the research consortium, known as ECOS, integrated cross-sectional data from 11 population-based cohorts in Australia, Canada, Estonia, Finland, the Netherlands, the United Kingdom, and the United States, covering 44 assessment waves collected between 1996 and 2023. In total, 786,557 participants aged four and above were classified, making this the largest clinical obesity prevalence study conducted to date.

The results reveal a striking age-dependent divergence between BMI-defined and clinical obesity. In early childhood, clinical obesity affected just 3.7 percent of children aged four to five, well below the 8.8 percent prevalence of BMI-defined obesity in the same group. Throughout childhood, adolescence, and early and mid-adulthood, BMI-defined obesity consistently overestimated the burden of clinically significant disease. At ages 35 to 44, for example, 26.3 percent of participants met BMI criteria for obesity, but only 15.1 percent met the Commission’s criteria for clinical obesity. Then the pattern inverts: from age 55 onward, clinical obesity becomes more common than BMI-defined obesity, climbing to 52.0 percent among adults aged 65 to 74.

The organ dysfunction criteria driving these classifications varied systematically with age. Among children with clinical obesity, elevated systolic blood pressure was overwhelmingly the most common finding, present in 87.3 percent of affected four- to nine-year-olds. Renal dysfunction, detected through microalbuminuria, was also most prevalent in childhood, affecting 44.2 percent of young children with clinical obesity. In early and mid-adulthood, liver dysfunction took center stage, with elevated alanine aminotransferase found in 56.3 percent of affected adults aged 20 to 34 and elevated gamma-glutamyl transferase in 48.8 percent of those aged 35 to 54. In later life, musculoskeletal dysfunction dominated, affecting 55.1 percent of people aged 75 and older with clinical obesity.

Sex emerged as a powerful modifier of these patterns. From adolescence through mid-adulthood, males carried a higher prevalence of clinical obesity than females; at ages 35 to 44, 18.6 percent of men versus 13.9 percent of women met the criteria. But from age 55 onward the relationship reversed, with women showing markedly higher prevalence. At ages 65 to 74, 57.1 percent of women had clinical obesity compared with 44.1 percent of men, and female prevalence peaked at 58.5 percent at ages 75 to 84. Preclinical obesity followed a different trajectory: in women it rose through early adulthood, peaked in the mid-thirties to mid-forties, and then declined, whereas in men it remained relatively constant across the life course. The authors suggest these divergences may partly reflect survival bias and differences in how excess adiposity manifests between the sexes, though the underlying biology remains to be fully explored.

Socioeconomic position, measured through education level, showed a more modest influence. Across all age groups, clinical obesity prevalence was slightly lower among people with high education compared with those in the middle and low education categories; at ages 65 to 74, prevalence was 46.8 percent in the high education group versus 53.9 and 55.0 percent in the middle and low groups respectively. The age-dependent patterns of both clinical and preclinical obesity were broadly similar across all three education strata, suggesting that while education shapes obesity risk, the relationship between excess fat and organ dysfunction follows a comparable life course architecture regardless of socioeconomic background.

The study also exposed how sensitive prevalence estimates are to the specific measures chosen to define excess adiposity. In a subgroup of cohorts with complete anthropometric and body composition data, waist-to-height ratio was met by virtually all participants classified with clinical or preclinical obesity, between 95.4 and 100 percent depending on the cohort, while body fat percentage was the least commonly satisfied criterion, met by as few as 9.6 percent of UK Biobank participants with clinical obesity. When excess adiposity was defined by any two anthropometric criteria, clinical obesity prevalence in adults ranged from 5.2 percent at ages 20 to 24 to 51.2 percent at ages 65 to 74, substantially higher than estimates based on BMI plus one anthropometric measure or body fat percentage alone. These differences carry real consequences for diagnosis, risk prediction, and treatment eligibility.

The authors are candid about the limitations inherent in retrofitting a new diagnostic framework onto data collected before it existed. No cohort captured all 13 diagnostic domains specified by the Commission, meaning clinical obesity prevalence was likely underestimated in some groups. Data on central nervous system, respiratory, lymphatic, and reproductive criteria were sparse or absent, and the researchers could not always verify that observed organ dysfunction was genuinely attributable to excess adiposity rather than to other common conditions of later life. Laboratory thresholds varied across jurisdictions, and the treatment of medicated conditions, such as hypertension controlled by antihypertensive drugs, required pragmatic decisions that the Commission’s guidelines do not address. The cohorts were also predominantly from high-income, majority-White populations, limiting generalizability to more diverse settings where the burden of obesity is growing fastest.

Despite these caveats, the consistency of the life course pattern across cohorts from different countries, recruitment epochs, and measurement protocols lends weight to the central conclusion: clinical obesity is rarer than BMI-defined obesity in childhood and early adulthood, but substantially more common in later life. The findings underscore an urgent need for prospective longitudinal studies with standardized collection of all diagnostic criteria, which would allow researchers to track how individuals transition from preclinical to clinical obesity and to determine whether early identification and intervention in childhood, a critical window for prevention, can alter that trajectory. For now, the study provides the most comprehensive picture yet of what the new definition of obesity means for real populations, and it suggests that the number on the scale, and even the ratio of weight to height, may be far less informative than the quiet damage that excess fat does to organs over decades of exposure.

Subject of Research: Life course prevalence of clinical and preclinical obesity using the Lancet Commission diagnostic criteria

Article Title: The lancet commission definition of clinical obesity: a multi-cohort cross-sectional analysis from early childhood to older age in seven high-income countries

Article References: Longmore, D. K., MacKechnie, G. P., Huntington, P. A., Chen, Z. H., de Groot, J., Mikkonen, S., Mykkänen, J., Pätsi, S., Puusepp, T., Fischer, K., Jaddoe, V., Kerr, J. A., Lakka, T. A., Lehtimäki, T., Miliku, K., Nedelec, R., Ponsonby, A.-L., Sebert, S., Vuillermin, P., … Viikari, J. (2026). The lancet commission definition of clinical obesity: a multi-cohort cross-sectional analysis from early childhood to older age in seven high-income countries. eClinicalMedicine, Article 104231. https://doi.org/10.1016/j.eclinm.2026.104231

Image Credits: AI Generated

DOI: 10.1016/j.eclinm.2026.104231

Keywords: clinical obesity, preclinical obesity, Lancet Commission, body mass index, organ dysfunction, life course epidemiology, adiposity, pediatric obesity, cohort study, prevalence, metabolic health, public health

The authors ground their argument in a conceptual shift that has been gathering force since the Lancet Commission on the Definition of Clinical Obesity published its diagnostic framework in 2025. That commission drew a sharp line between preclinical obesity, a state of elevated risk in which organs still function normally, and clinical obesity, an established disease in which excess adiposity has begun to damage organs or limit physical function. This is not semantic hair-splitting. The distinction determines who needs what, and when. A patient with preclinical obesity may be well served by lifestyle support and, in some cases, medication to prevent progression. A patient with clinical obesity, whose joints, liver, heart, or metabolism are already failing under the burden of diseased fat tissue, may need interventions powerful enough to reverse established organ dysfunction, and quickly.

Cohen and his colleagues contend that failing to make this distinction carries four concrete harms. First, clinicians may delay escalating treatment for patients with clinical disease, the very group that benefits most from definitive therapy, while they wait to see whether a drug trial will succeed. Second, patients at the preclinical stage risk over-medicalization, receiving intensive and costly interventions they do not yet require. Third, when clinical trials enroll undifferentiated populations that mix these two states, the measured treatment effects become diluted, obscuring which therapy truly helps whom. Fourth, health systems with finite resources end up spending them inefficiently, funding interventions for people who would have done well with less while rationing them from people whose disease demands more. The positioning of surgery, in other words, is not an organizational detail but a question with direct clinical and economic stakes.

So what does the evidence say surgery can still deliver? The authors describe metabolic bariatric surgery as remaining among the most durable interventions available for clinical obesity. Operations such as sleeve gastrectomy and gastric bypass do more than restrict intake; they alter gut hormone signaling, appetite regulation, and glucose metabolism in ways that reduce adiposity, improve organ function, and, in a substantial fraction of patients, drive remission of obesity-related conditions including type 2 diabetes. Where a daily injectable drug works only for as long as it is taken, a surgical intervention produces anatomical and hormonal changes that persist. Long-term observational cohorts and randomized trials have documented weight loss and cardiometabolic benefit extending well beyond a decade after operation, a horizon no current pharmacotherapy has matched in head-to-head comparison.

The safety picture has also changed almost beyond recognition. The perspective emphasizes that over the past three decades surgical practice has evolved through technical refinement, standardized protocols, and systematic perioperative optimization. Contemporary bariatric surgery, supported by randomized clinical trials and mature long-term observational datasets, is described by the authors as a very safe therapeutic option for patients with advanced obesity and complex metabolic disease. Mortality rates for modern procedures are comparable to those of routine general surgery such as gallbladder removal, a statistic that surprises many clinicians whose mental image of the field was formed in an earlier era. The operations themselves have been refined laparoscopically and, increasingly, robotically, with shorter hospital stays and fewer complications than the open procedures of the 1990s.

Yet the authors do not dismiss the new pharmacotherapy; quite the opposite. Their argument is that glucagon-like peptide-1 receptor agonists and related agents are legitimate, powerful tools that belong inside a multimodal treatment framework, not rivals to be defeated. The framework they envision integrates behavioral, pharmacological, endoscopic, and surgical interventions, matched to disease stage and adapted over time. A patient might begin with structured lifestyle change and medication, add an endoscopic or pharmacological escalation if response is inadequate, and proceed to surgery when clinical obesity is established or when pharmacotherapy fails, is not tolerated, or is discontinued. Surgery, in this model, is not the option of last resort after everything else has failed, nor the reflexive first move. It is one instrument in a staged repertoire, deployed according to disease severity and patient goals.

The real-world behavior of patients on the new drugs adds urgency to this reasoning. A 2025 analysis in JAMA Network Open tracked discontinuation and reinitiation of dual-labeled GLP-1 receptor agonists among United States adults with overweight or obesity and documented substantial rates of patients stopping their medication, a pattern consistent with the well-known challenges of cost, supply, side effects, and waning motivation that accompany chronic injectable therapy. Weight regain after discontinuation is a predictable consequence of stopping an appetite-suppressing drug, because the underlying biology of obesity has not changed. The authors point to this fragility of pharmacological maintenance as precisely the scenario in which a durable intervention such as surgery retains its value, either as primary therapy for selected patients or as a rescue strategy after pharmacotherapy-induced weight loss plateaus or reverses. The International Federation for the Surgery of Obesity has already issued a formal statement, co-authored by several of the same authors, addressing how to position surgery after drug-induced weight loss in patients with clinical obesity.

Economics complicates the picture further. Two recent analyses cited in the perspective tackle the cost question directly. A matched cohort study published in Surgery for Obesity and Related Diseases in 2025 examined the cost-effectiveness of bariatric surgery and found grounds for arguing that surgical treatment pays for itself over time through reduced management of diabetes, cardiovascular disease, and other obesity complications. A separate cost comparison in Surgical Endoscopy asked where the break-even point lies between GLP-1 receptor agonists and surgery, a question that becomes pointed when a medication must be taken indefinitely at an annual cost that can exceed the one-time price of an operation within a few years. Health systems cannot fund everything for everyone, and the authors argue that stage-adapted care, in which expensive definitive therapy is reserved for established clinical disease, is the most defensible way to allocate limited resources while still offering earlier, less intensive support to those at risk.

Digital therapeutics form the final piece of the multimodal puzzle. A randomized controlled trial published in the same journal in 2026 evaluated a digital health application for weight management in people with obesity and reported six-month efficacy results, illustrating how digitally enabled care pathways are being woven into the therapeutic landscape alongside drugs and surgery. The authors view these tools not as competitors but as connective tissue: platforms that can extend behavioral support, monitor patients after surgery, flag weight regain, and coordinate escalation between treatment modalities. In an integrated system, a patient’s care might move fluidly between an app, a prescribing physician, an endoscopist, and a surgeon, with each step justified by measured disease status rather than by the habits or incentives of any single specialty.

The perspective’s ultimate message is a call for clinical discipline in a moment of therapeutic enthusiasm. Effective drugs have not made surgery obsolete, and surgery has not made drugs unnecessary; instead, the new diagnostic framework of clinical obesity gives clinicians a principled way to decide which patient needs which tool, and when. Mispositioning surgery, the authors warn, will delay definitive treatment for the sickest patients, while abandoning pharmacotherapy would deny many others a safer, less invasive path. The task for the coming decade is to build care pathways that treat obesity as the heterogeneous, chronic, progressive disease it is, matching the durability of the scalpel and the flexibility of the syringe to the stage of the disease in front of the clinician. In that matching, the authors conclude, lies the future of obesity medicine.

Subject of Research: Positioning of metabolic bariatric surgery within multimodal obesity care in the era of effective pharmacotherapy

Article Title: Where does surgery fit in the era of effective obesity pharmacotherapy? Positioning metabolic bariatric surgery within multimodal obesity care

Article References: Cohen, R. V., Salminen, P., Ponce, J., & Prager, G. (2026). Where does surgery fit in the era of effective obesity pharmacotherapy? Positioning metabolic bariatric surgery within multimodal obesity care. International Journal of Obesity. https://doi.org/10.1038/s41366-026-02215-y

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DOI: 10.1038/s41366-026-02215-y

Keywords: obesity, bariatric surgery, metabolic surgery, GLP-1 receptor agonists, pharmacotherapy, clinical obesity, Lancet Commission, multimodal treatment, digital health, cost-effectiveness, weight regain, International Journal of Obesity

The analogy is more than rhetorical. Cardiovascular medicine underwent its own conceptual revolution after discovering that the sheer size of an atherosclerotic plaque poorly predicts who will have a heart attack. Many severely narrowed arteries remain silent for life, while acute events often arise from lesions causing only modest narrowing. What matters is not the presence of plaque but its biological behavior: inflammatory activity, lipid composition, the integrity of the fibrous cap, neovascularization, intraplaque hemorrhage, endothelial dysfunction, and thrombotic susceptibility. Cardiovascular risk is now understood as a dynamic interplay between the pathological substrate and systemic modifiers, including age, genetics, hypertension, diabetes, dyslipidemia, obesity, smoking, chronic inflammation, physical inactivity, diet, and environmental exposures. Plaque detection marks increased biological risk, not an inevitable cardiac event.

Alzheimer’s disease, the authors argue, has reached the same stage of conceptual maturity. Amyloid accumulation may initiate or facilitate downstream processes, but the transition from biological pathology to clinical dementia is shaped by their interaction with tau propagation, neuroinflammation, synaptic dysfunction, cerebrovascular injury, metabolic alterations, genetic susceptibility, co-existing pathologies, and mechanisms of resilience. Within this framework, amyloid remains indispensable to the biological definition of Alzheimer’s disease, but its clinical significance depends on the biological context in which it occurs. This multidimensional view helps explain why individuals with comparable amyloid burden can follow markedly different trajectories, and why amyloid positivity alone does not equate to clinical Alzheimer’s disease.

Some of the strongest evidence that amyloid and dementia can be uncoupled comes, paradoxically, from the population in which the amyloid cascade hypothesis is best supported: carriers of autosomal dominant Alzheimer’s mutations. In the Colombian PSEN1 E280A kindred, the largest such family in the world, affected members typically develop mild cognitive impairment around age 44 and dementia around age 49, with amyloid deposition detectable more than two decades before symptoms. Yet within this genetically homogeneous cohort, two carriers have been reported who accumulated amyloid burdens comparable to or exceeding those of their symptomatic relatives but remained free of dementia for decades beyond the expected age of onset. One, homozygous for the rare APOE3 Christchurch variant, showed high amyloid-PET signal but limited tau spread and cortical atrophy, and did not develop dementia until her seventies, roughly three decades later than expected. A second, carrying a rare RELN variant, showed a similarly protected trajectory. In both cases, protection appears to act downstream of amyloid, limiting tau propagation and the associated neuroinflammatory and neurodegenerative cascade.

This principle extends well beyond rare genetic forms of the disease. Population-based cohorts and biomarker studies consistently show that a substantial proportion of cognitively unimpaired older adults fulfill biological criteria for Alzheimer’s disease while remaining clinically normal for prolonged periods. A meta-analysis of biomarker-defined cohorts found that amyloid positivity increased the risk of clinical progression, but that this risk rose markedly when concomitant tau pathology was present. Amyloid positivity, in other words, identifies a state of increased biological susceptibility rather than an inevitable clinical destiny, much as plaque presence flags vascular risk without dictating a heart attack.

Therapeutic trials reinforce the same lesson. Anti-amyloid monoclonal antibodies such as lecanemab and donanemab have unequivocally demonstrated that cerebral amyloid can be substantially reduced in living brains. Across pivotal Phase III trials, treatment slowed cognitive decline but did not arrest disease progression, and clinical benefits have been consistently modest relative to the magnitude of amyloid removal. The authors caution that these results should not be read as a failure of the amyloid hypothesis. Rather, they suggest that amyloid removal alone may be insufficient once downstream cascades, including tau spread, synaptic dysfunction, neuroinflammation, and neuronal loss, have become established. Modifying the pathological substrate does not necessarily abolish the network of mechanisms ultimately responsible for cognitive decline, just as clearing one plaque does not eliminate the systemic biology of cardiovascular disease.

Community-based neuropathological studies add a further, often underappreciated, dimension. Unlike clinic-based autopsy series, cohorts such as the Religious Orders Study, the Rush Memory and Aging Project, and the Medical Research Council Cognitive Function and Ageing Study examine brains irrespective of ante-mortem diagnosis, offering a more representative picture of brain aging. These studies consistently show that pure Alzheimer’s disease is the exception rather than the rule in older adults. Most individuals with dementia harbor multiple co-existing pathologies, including cerebrovascular disease, Lewy body pathology, limbic-predominant age-related TDP-43 encephalopathy, hippocampal sclerosis, and argyrophilic grain disease. Crucially, co-pathologies are not incidental: each additional pathology lowers the threshold of Alzheimer’s neuropathologic change required for clinically overt dementia, while individuals with substantial amyloid but limited co-existing disease may remain cognitively preserved.

The authors also elevate the concept of biological resilience, distinguishing it from brain reserve, the structural capacity to tolerate pathology, and cognitive reserve, the ability to sustain performance through more efficient neural networks shaped by education and cognitive engagement. Biological resilience refers instead to intrinsic molecular, cellular, vascular, and immunological mechanisms that limit the pathological consequences of Alzheimer’s disease despite the presence of its defining lesions. Evidence is accumulating rapidly: the protected Colombian carriers demonstrate that extensive amyloid can coexist with preserved cognition when tau spread is restrained, and genetic modifiers such as APOE, RELN, and microglial genes like TREM2 show that resilience is partly biologically encoded. Resilience likely emerges from the interaction of many systems, including tau propagation control, synaptic integrity, innate immune regulation, blood-brain barrier maintenance, cerebrovascular health, mitochondrial function, proteostasis, and metabolic homeostasis.

This framework also reframes the meaning of modifiable risk factors. The 2024 Lancet Commission on dementia prevention identified 14 potentially modifiable factors, including lower educational attainment, hearing loss, high LDL cholesterol, depression, traumatic brain injury, physical inactivity, diabetes, smoking, hypertension, obesity, excessive alcohol consumption, social isolation, air pollution, and untreated vision loss. Viewed through the new lens, these are not merely contributors to dementia risk but determinants of the brain’s resilience or vulnerability to Alzheimer’s pathology. Hypertension, diabetes, obesity, dyslipidemia, smoking, and air pollution promote endothelial dysfunction, blood-brain barrier impairment, cerebrovascular injury, oxidative stress, and chronic inflammation, lowering the threshold at which amyloid translates into neuronal dysfunction. Conversely, education, cognitive stimulation, physical activity, social engagement, and preserved sensory function help the brain tolerate pathological burden. The parallel with cardiology is direct: plaque identifies the underlying disease, but systemic risk factors determine whether it ever produces an event.

The practical implication is a shift from biological diagnosis to biological risk stratification. Current NIA-AA criteria answer with remarkable precision whether an individual has biological Alzheimer’s disease, but they are not designed to answer who will progress, when, or through which pathways. The authors propose that once biological Alzheimer’s disease is established, clinical decision-making should integrate amyloid and tau biomarkers with measures of neurodegeneration, cerebrovascular injury, co-existing proteinopathies, neuroinflammation, genetic susceptibility, metabolic health, and cognitive reserve to estimate the probability and pace of clinical conversion. The next frontier, they conclude, is not to move beyond amyloid but to move beyond an amyloid-centric interpretation of the disease. If amyloid defines the biological identity of Alzheimer’s disease, resilience may ultimately define its clinical destiny, and integrating pathological burden with the determinants of resilience and vulnerability could provide the foundation for truly personalized prediction, prevention, and treatment.

Subject of Research: A conceptual framework comparing Alzheimer's disease progression beyond amyloid pathology with atherosclerosis risk biology

Article Title: Alzheimer's Disease Beyond Amyloid: Lessons From Atherosclerosis

Article References: Ciaccio, M., & Agnello, L. (2026). Alzheimer's Disease Beyond Amyloid: Lessons From Atherosclerosis. Annals of Clinical and Translational Neurology, Article acn3.70533. https://doi.org/10.1002/acn3.70533

Image Credits: AI Generated

DOI: 10.1002/acn3.70533

Keywords: Alzheimer's disease, amyloid, tau, atherosclerosis, biological resilience, biomarkers, neuroinflammation, cerebrovascular disease, Lancet Commission, anti-amyloid therapies, mixed neuropathology, precision medicine