Implications of a New Obesity Definition Among the All of Us Cohort.

Importance: A recent Lancet Commission proposed an obesity definition that integrates body mass index (BMI [calculated as weight in kilograms divided by height in meters squared]) with anthropometric measures, marking a paradigm shift in how obesity is conceptualized and classified. Objective: To determine the clinical implications of the new definition of obesity. Design, Setting, and Participants: This population-based longitudinal cohort study leveraged data from the All of Us cohort. Participants in All of Us with complete anthropometric data were enrolled between May 31, 2017, and September 30, 2023, with a median follow-up of 4.0 (IQR, 1.7-4.7) years. Exposure: Obesity classified by traditional and new definitions. Main Outcomes and Measures: Obesity was defined by the new framework using sex- and race-specific thresholds as (1) BMI above the traditional obesity threshold plus at least 1 elevated anthropometric measure or BMI greater than 40 (BMI-plus-anthropometric obesity) or (2) at least 2 elevated anthropometric measures with BMI below the traditional obesity threshold (anthropometric-only obesity). Obesity was categorized as clinical or preclinical based on organ dysfunction and/or physical limitation. Results: Among 301 026 individuals (183 633 [61.0%] female; median age, 54 [IQR, 38-65] years), 206 361 (68.6%) had obesity according to the new definition vs 128 992 (42.9%) according to the traditional definition, due to inclusion of individuals with anthropometric-only obesity. Among the overall cohort, 108 650 individuals (36.1%) had clinical obesity according to the new definition; this prevalence increased with age, as 24 498 of 45 018 individuals 70 years or older (54.4%) had clinical obesity. Compared with no obesity, odds ratios of organ dysfunction were 3.31 (95% CI, 3.24-3.37) for BMI-plus-anthropometric obesity and 1.76 (95% CI, 1.73-1.80) for anthropometric-only obesity per the new definition. In longitudinal analyses, clinical obesity conferred elevated risks of incident diabetes (adjusted hazard ratio [AHR], 6.11; 95% CI, 5.67-6.60), cardiovascular events (AHR, 5.88; 95% CI, 5.38-6.43), and all-cause mortality (AHR, 2.71; 95% CI, 2.41-3.05) compared with no obesity or organ dysfunction. Preclinical obesity was also associated with increased risks of incident diabetes (AHR, 3.32; 95% CI, 3.08-3.58) and cardiovascular events (AHR, 1.40; 95% CI, 1.27-1.55), albeit to a lesser degree. Conclusions and Relevance: In this cohort study, adoption of the new definition of obesity significantly increased obesity prevalence with major implications for clinical practice and public policy. The new framework effectively stratified individuals at high risk of organ dysfunction and long-term complications while introducing anthropometric-only obesity and preclinical obesity as distinct entities warranting further study.