Body mass index in young men in Switzerland after the national shutdowns during the COVID-19 pandemic – Results from a cross-sectional monitoring study at population level since 2010

Background: Due to the COVID-19 pandemic, the Swiss Federal Council imposed a shutdown twice, which may have changed dietary and physical activity habits. On the question of weight change during the pandemic, there is little information based on measured weight data. In this study, we investigate whether the body mass index (BMI) of young Swiss men conscripted after the two shutdown periods in Spring and Fall 2020 differed from the conscripts examined before the shutdowns.Methods: We are analysing body measurements of young Swiss men taken during mandatory recruitment for the Swiss Armed Forces on the cross-sectional (not individual longitudinal) monitoring level and across weeks of conscription between January 2010 and July 2021 (n=373,016). These cross-sectional data allow for continuous health monitoring of young men almost at the population level (coverage >90% of recruitment relevant age categories). For statistical modelling, we use GAM (Generalized Additive Model framework.Results: We showed that the BMI of conscripts who were examined in the 15 weeks after the two shutdowns in Spring and Autumn 2020 was not or only weakly different from baseline. Sensitivity analyses showed that this conclusion also holds if assessing the BMI distribution or the prevalence of overweight and/or obesity. The GAM models further showed strong effects of individual and area-based SEP as well as age on BMI.Conclusion: Our results suggest that any lifestyle changes during the pandemic in young men may have been too modest to be clearly reflected in body weight (suggesting small or none effect). However, longitudinal data and/or data on women, children, or the elderly may lead to different conclusions.