Assessing obesity beyond body mass index: Integrating physiological and functional indicators of impairment in national health surveillance.

Background: Body mass index (BMI) is commonly used to estimate obesity prevalence; however, reliance on BMI alone can lead to an incomplete understanding of obesity's impact on health. In line with the 2025 recommendations of the Lancet Diabetes & Endocrinology Commission, this study combines population-level measures of excess adiposity with indicators of physiological dysfunction and activity limitation across eight body system domains to characterize clinical and preclinical obesity among Canadian adults.

Data and methods: Measured and self-reported data from the 2016 to 2019 Canadian Health Measures Survey were used to define excess adiposity as measured BMI in the obese range plus elevated waist circumference. A three-tier system was used to capture progressive obesity-related impairment. At each tier, clinical obesity was defined by excess adiposity and indicators of impairment in one or more domains (Tier 1), two or more domains (Tier 2), or three or more domains (Tier 3). Preclinical obesity at each tier was characterized by excess adiposity with fewer indicators of impairment than the corresponding clinical thresholds. Prevalence estimates for these indicators and characterizations of obesity were calculated by sex and age group.

Results: Just over one in four Canadian adults had excess adiposity. Prevalence of physiological dysfunction and activity limitation indicators varied across domains and sex and age groups. Clinical and preclinical obesity prevalences were 19% and 8% at Tier 1, 12% and 15% at Tier 2, and 7% and 20% at Tier 3, respectively. Preclinical obesity - especially at tiers 1 and 2 - was more common in younger adults and females.

Interpretation: Younger adults and females with excess adiposity were less likely to present with obesity-related physiological dysfunction or activity limitation, indicating early stage impairment and highlighting opportunities for targeted prevention. Integrating measures of impairment when assessing obesity can refine population surveillance efforts.