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Researchers say they saw an increase of about eight per cent over the first 11 years of the study, from 2009 to 2020, compared to an increase of more than 1 percentage point a year between 2020 and 2023.

That’s about twice the pre-pandemic rate of increase. 

Laura Anderson, the study’s author and an associate professor at McMaster University, says these findings suggest public health restrictions during the COVID-19 pandemic may have had an impact on obesity rates.

Anderson says there was a “steep increase� in obesity rates among young adults, particularly young females, who showed an increase of 4.7 per cent between 2020 and 2023 in the youngest age group. 

Dr. Mélanie Henderson, a pediatric endocrinologist and researcher at the CHU Sainte-Justine, says the closure of gyms, extracurricular programs, schools and workplaces led to an absence of structure, extra screen time and closer proximity to the fridge. 

“It was kind of the perfect storm,” says Henderson, who had no connection to the study. She adds that adolescence is a vulnerable time that could have made younger adults more susceptible to pandemic conditions. 

The study also suggests that stress related to changes in job status or caregiving may have led to weight gain for some. 

But it also says further study is needed to better understand the causes and how they can be prevented in the future. 

Henderson says the first step is creating policies that ensure health-care services are available to treat and manage obesity.

This report by The Canadian Press was first published July 14, 2025. 

Canadian Press health coverage receives support through a partnership with the Canadian Medical Association. CP is solely responsible for this content.