Five years after the start of the COVID-19 pandemic, a new study is shedding light on the impact of associated public health restrictions on Canadians’ waistlines. 

The study, led by McMaster University researchers, shows the prevalence of obesity in Canada increased faster in the four years after the start of the pandemic compared to the previous 11 years, especially in younger adults. The findings were published in CMAJ (Canadian Medical Association Journal) on July 14, 2025.  

Obesity is a risk factor for a range of diseases and can negatively affect a person’s health and well-being as well as increase the burden on the health care system. However, the authors caution that efforts to address rising rates of obesity should consider unintended impacts of weight control messaging on weight stigma.  

“The pandemic disrupted many aspects of daily life, including routines around eating, physical activity, and stress management,” said Laura Anderson, senior author of the study and associate professor in the Department of Health Research Methods, Evidence and Impact at McMaster.   

“Our findings show that these disruptions had a measurable impact on Canadians’ health, particularly among young adults and women. This underscores the need for targeted, equitable strategies to support healthy living and address the long-term consequences of the pandemic,” adds Anderson, co-director of the Centre for Health Economics and Policy Analysis (CHEPA) at McMaster.  

The study included data on 746,250 adults aged 18 and over and looked at trends in body mass index (BMI) over 15 years, from 2009 to March 2020 and from April 2020 to December 2023. Researchers found: 

• BMI-defined obesity rates increased from 25 per cent in 2009 to 33 per cent in 2022, an absolute increase of about eight per cent.  

• After the pandemic started, obesity increased by just over one percentage point a year, about twice the pre-pandemic rate of increase.  

• Obesity rates in males and females narrowed, with a nine per cent increase in obesity in females compared with a seven per cent increase in males.  

• Obesity rates were highest in people who were White or Black. 

“We saw notable shifts in groups that historically had lower obesity rates, particularly young adults and women,” said Anderson. “The substantial increases in these populations during the pandemic raise important concerns about long-term health impacts and highlight the need for tailored prevention and support strategies.” 

The researchers observed a small increase in underweight adults during the study period and note that being underweight can have negative health effects. Investment in research and approaches to obesity prevention and treatment are needed and should be a priority for funders and policymakers. 

The research was supported by a grant from the Canadian Institutes of Health Research and an Ontario Research Chair in Health Human Resources, funded by an endowment to McMaster University from the Ontario Ministry of Health.