The COVID-19 pandemic was associated with a modest but significant excess BMI increase of 0.21 kg/m² and 1.06 times higher odds of obesity among Canadian adults compared with prepandemic trends.
Key Findings
Results
Participants measured during the pandemic had a statistically significant excess BMI increase compared with prepandemic trends.
Excess BMI increase during the pandemic was 0.21 kg/m² (95% CI 0.15 to 0.28)
A significant interaction was found between follow-up time and timing of FUP2 data collection (before or during the pandemic)
33% of Follow-up 2 data (n=13,444) was gathered after 16 March 2020, when COVID-19 restrictions began
Weighted generalised estimating equations were used to assess BMI changes before and during the pandemic
Correction factors were applied for self-reported BMI
Results
Participants measured during the pandemic had significantly higher odds of obesity compared with prepandemic trends.
Odds of obesity were 1.06 times higher (95% CI 1.03 to 1.09) during the pandemic compared with prepandemic trends
BMI-defined obesity was measured at baseline, follow-up 1, and follow-up 2
The study included 41,302 adults aged 45–85 at baseline participating in the Canadian Longitudinal Study on Aging (CLSA)
The prospective cohort design allowed for comparison of within-person BMI trajectories before and during the pandemic
Results
The pandemic-associated BMI increase was more pronounced among females compared with males.
Subgroup analyses explored how the association between COVID-19 and BMI varied by sociodemographic and health status
Sex was identified as a modifier of the pandemic's impact on BMI and obesity
The paper describes increases as 'more pronounced among females'
Results
Middle-aged adults showed more pronounced pandemic-associated BMI increases compared with older age groups.
The study sample spanned adults aged 45–85 at baseline
Age was identified as a moderating factor of the pandemic's impact on BMI
The paper describes increases as 'more pronounced among middle-aged adults'
Results
Adults without diabetes experienced more pronounced pandemic-associated BMI increases compared with those with diabetes.
Diabetes status was examined as a health status modifier of the COVID-19 pandemic's association with BMI
The paper describes increases as 'more pronounced among those without diabetes'
Health status was one of several sociodemographic and health variables used to explore heterogeneity of the pandemic's impact
Methods
The study used a prospective cohort design with a large nationally representative Canadian sample to assess pandemic-related BMI changes.
The Canadian Longitudinal Study on Aging (CLSA) included 41,302 adults aged 45–85 at baseline
BMI was measured at three time points: baseline, follow-up 1, and follow-up 2
COVID-19 restrictions in Canada began on 16 March 2020, which served as the cutoff for defining pandemic-era data collection
Weighted generalised estimating equations were used to account for the complex survey design and assess longitudinal BMI trajectories
What This Means
This research suggests that the COVID-19 pandemic was associated with small but measurable increases in body weight among Canadian adults aged 45 to 85. Using data from a large, long-running national study of aging, researchers compared how participants' body mass index (BMI) changed before the pandemic versus during it. People who had their measurements taken after pandemic restrictions began in March 2020 gained about 0.21 kg/m² more in BMI than would have been expected based on pre-pandemic trends, and were about 6% more likely to be classified as obese.
The weight gains were not the same for everyone. Women, middle-aged adults, and people without diabetes tended to experience larger pandemic-related BMI increases than other groups. This suggests that the pandemic's effects on lifestyle factors like physical activity, diet, and daily routines may have disproportionately affected certain segments of the population.
This research matters because even modest increases in BMI and obesity rates at a population level can have significant public health consequences, including higher rates of chronic diseases like heart disease and type 2 diabetes. The authors note that ongoing research is needed to understand whether these changes persisted or worsened after the acute pandemic period, and to identify which populations may need the most support in maintaining healthy weight over the long term.
Sakib M, Griffith L, Erbas Oz U, Basta N, Gerstein H, Morgenstern J, et al.. (2026). Impact of the COVID-19 pandemic on obesity: a prospective cohort study of the Canadian Longitudinal Study on Aging (CLSA).. BMJ open. https://doi.org/10.1136/bmjopen-2026-116378