Effect of the COVID-19 Epidemic on Body Mass Index: Findings from a Large Survey during Wuhan Lockdown

This study aimed to explore the effect of the Wuhan lockdown on body mass index (BMI) among Wuhan residents as well as factors including food habits affected and changes in physical activity mediating the association. As a survey of the Wuhan lockdown, a random digit dialing method was used to sample residents aged 18 years and older. A computer-aided telephone interview was applied to survey 11,223 residents in Wuhan City in July 2020. Ordinary least squares (OLS) regression and mediation analysis were used to analyze the influence of the Wuhan lockdown on BMI. Demographic characteristics, lifestyle characteristics, and health status differed statistically significantly between residents living in and those who left Wuhan during the lockdown (mean BMI, 23.05 +/- 0.04 kg/m(2) and 22.34 +/- 0.06 kg/m(2), respectively). The mean BMI among residents living in Wuhan was 0.42 kg/m(2) higher (P < 0.001) than that of residents who left Wuhan during the lockdown, as determined by multivariate OLS regression analysis. Residents living in Wuhan during the lockdown had higher BMI among those aged 18-29 and 30-44 years (P < 0.001), with no difference among those aged 45+ years. The association between living in Wuhan and increased BMI was the strongest among residents who were overweight/obese. The mediation analysis results showed an indirect effect path with living in Wuhan (through decreased physical activity and increasing BMI) and the direct effect of living in Wuhan during the lockdown. The lack of association between living in Wuhan and increased BMI among residents aged 45+ years was due to the indirect influence of living in Wuhan affecting food habits. The findings indicated that the lockdown in Wuhan city increased residents' BMI, especially among those who were young or overweight/obese, partly because of decreased physical activity.