More adults in the United States weighed in as obese during the first year of the coronavirus pandemic than in the year before the pandemic began.

To get a clearer picture of just how much weight Americans gained, a researcher from the U.S. Department of Agriculture looked at data on more than 3.5 million people who participated in the 2011-2020 Behavioral Risk Factor Surveillance System, a nationally representative survey of U.S. adults 20 years old or older.

The analysis provided further evidence of an increase in obesity rates among many Americans during the first year of the pandemic and explained changes in health behaviors that resulted in weight gain.

Obesity rates were three percent higher during the year beginning in March 2020 compared to 2019 and the pre-pandemic 2020 period. The body mass index increased by an average of almost one percent.

The findings offer a snapshot of the scope and sources of adult obesity in the U.S. and could help guide health policy. “Our results contribute additional insights that can serve to inform policymakers about the state of the U.S. adult obesity epidemic and obesity-related risk factors,” the study’s author, Brandon Restrepo, said.

The survey asked for information about a participant's health, their risk behaviors, use of preventive services and chronic diseases. The analysis controlled for factors such as age, sex, race/ethnicity, education level, household income, marital status, number of children and state of residence.

Obesity rates were three percent higher during the year beginning in March 2020 compared to 2019 and the pre-pandemic 2020 period.

Four obesity-related behaviors changed significantly among U.S. adults, during the pandemic: exercise, sleep duration, alcohol consumption and smoking. Adults who reported weight gain also reported more frequent snacking and eating more in response to sight, smell and stress.

The rate of exercise increased by more than four percent and sleep duration increased by more than one percent. So why did rates of obesity climb, too?

More exercise and more sleep are usually associated with weight loss, but these increases were not enough to offset the almost three percent increase in the number of days in which alcohol was consumed and the four percent decrease in smoking. As a result, the national body mass index increased by an average of almost one percent during the pandemic.

Future studies could drill deeper into our eating habits during the pandemic, Restrepo, a member of the USDA Economic Research Division, said. For example, it may be that adults began to consume more calorie-dense foods; and since obesity affects some adults more than others, it would also be helpful to look at changes in obesity rates in different demographic and socioeconomic groups.

The study is published in the American Journal of Preventive Medicine.