Trends in obesity defined by body mass index among adults before and during the COVID-19 pandemic: a repeated cross-sectional study of the 2009-2023 Canadian Community Heath Surveys.

Publication date: Jul 13, 2025

The COVID-19 pandemic affected health behaviours and the social determinants of health. We sought to describe trends in the prevalence in body mass index (BMI) categories before and during the COVID-19 pandemic among adults in Canada. We conducted a repeated cross-sectional study of adults in the 2009-2023 Canadian Community Health Surveys. We compared changes after the onset of the COVID-19 pandemic (April 2020 to December 2023) to an 11-year prepandemic period (January 2009 to March 2020). We calculated odds ratios (ORs) and absolute percentages from, respectively, weighted logistic and linear regression models. Our unweighted analytic sample included 746 250 adults from the 2009-2023 surveys. The prevalence of BMI-defined obesity increased from 24. 95% in 2009 to 32. 69% in 2023 (absolute increase 7. 74%). The COVID-19 pandemic period was associated with an adjusted annual increase in the relative odds of obesity that was 1. 02 (95% confidence interval [CI] 1. 01-1. 04) times greater than the prepandemic period. The absolute rate of increase of BMI-defined obesity nearly doubled during the pandemic, with an annual average excess rate of 0. 44 (95% CI 0. 14-0. 74) percentage points. Class II and III obesity increased at a greater absolute rate than class I, indicating a shift toward more severe obesity. The relative increase in class III obesity was greater among young adults and females. Since the COVID-19 pandemic, the prevalence of BMI-defined obesity, and especially class III obesity, increased at a faster rate than before the pandemic. Some groups that historically had lower levels of obesity were disproportionately affected during the pandemic.

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