Jinho Kim,Gum-Ryeong Park,Taehoon Kim
The Gendered Impacts of COVID-19 on Adolescent Body Mass Index in South Korea: Evidence and Mechanisms
The Gendered Impacts of COVID-19 on Adolescent Body Mass Index in South Korea: Evidence and Mechanisms

School closures and social distancing measures during the COVID-19 pandemic have greatly changed the lives of adolescents. Specifically, adolescents’ physical activity, dietary habits, sedentary behavior, and stress are expected to have changed after COVID-19. These changes can in turn affect their health, including increasing the risk of obesity. The changes in health-related behaviors may differ between male and female students. Using large-scale, nationally representative data, this study examines whether the impacts of COVID-19 on body mass index (BMI) and obesity in adolescents differ by gender. This study also sheds light on potential mechanisms for explaining the possibly gendered consequences of the pandemic for BMI and obesity among adolescents.

This study uses the Korea Youth Risk Behavior Web-based Survey’s repeated cross-sectional data that examine the health and health behaviors of students. The sample consists of 141 511 middle school students who were surveyed during the years 2017-2021. Two major dependent variables include log BMI and obesity. We considered changes in physical activity, sedentary behaviors, diet, and stress as mechanisms by which the COVID-19 pandemic affects adolescents’ body weight. Using the multivariate regression, we estimate how the dependent and mechanism variables differentially changed by gender after COVID-19.

Table 1 shows summary statistics for all students and by gender. Boys have higher BMI, obesity rates, physical activity levels, and rates of eating fattening foods than girls. The proportion of students who usually feel stressed is higher among girls. Table 2 shows the estimation results. Column (1) presents the effects of COVID-19 on girls’ outcomes. Column (2) shows the additional effect for boys, that is, the effects of COVID-19 on boys’ outcomes are the sum of the estimates in columns (1) and (2). Panel (a) shows that the BMI of girls decreased by 0.7% after COVID-19, whereas the BMI of boys increased by 3.2% (–0.7 + 3.9). The obesity rate increased by 4.3 percentage points for boys, and it decreased by 0.8 percentage points for girls. Panel (b) shows that the proportion of students who did long- and medium-intensity exercise four times or more in the past 7 days decreased by 2.9 percentage points for girls. The reduction was 7.6 percentage points for boys. Second, the proportion of girls who did high-intensity exercise four times or more in the past 7 days decreased by 5.3 percentage points. The decrease was 7.0 percentage points for male students. Third, the mean total sitting time per day increased by 34.42 minutes for boys, while it did not significantly change for girls. Panel (c) shows that the proportion of girls who had fast food at least three times in the past week decreased by 2.9 percentage points. The reduction was 1.8 percentage points for boys. The proportion of students who drank carbonated beverages at least three times in the past week decreased by 2.7 percentage points for girls and 2.0 percentage points for boys. The proportion of students who drank sugary beverages decreased by 7.7 percentage points for girls and 5.1 percentage points for boys. Panel (d) presents that the ratio of girls who usually felt stress decreased by 5.0 percentage points. For boys, it decreased by 2.7 percentage points.

Previous studies reported that COVID-19 has put adolescents at higher risks of physical health problems, but less attention has been paid to the extent to which gender moderates the link between the pandemic and adolescent physical health and health behaviors. We found that the levels of BMI and the risk of obesity have significantly increased for boys after COVID-19, while they slightly decreased for girls. We also documented a larger decrease in physical activity among boys than girls and an increase in sitting time only among boys. Not only does school closure prevent boys from gathering for a group activity, but also social distancing strictly restricts the use of gyms. Given that physical activities among boys are largely group-based, the pandemic may have limited boys’ physical activity to a larger extent. This may, in turn, have a greater impact on boys’ sitting time than girls’ sitting time. Girls’ preference for sedentary activities, rather than group activities with peers, may leave little change in their sitting time. We found a somewhat surprising finding that the consumption of fattening foods decreased after COVID-19. These results are inconsistent with previous findings that the pandemic causes increased consumption of unhealthy foods such as fast food, candy, and soda. Possible explanations may be that (1) reduced stress due to decreased academic burden during the pandemic may contribute to lower consumption of fattening foods, (2) parents who stay longer at home (eg, working from home) may maintain regular healthy eating habits for their children throughout homemade meals, and (3) school closure may reduce opportunities for young children to snack with friends. Therefore, taken together, we argue that the impact of COVID-19 on boys’ BMI and obesity risk is likely to operate through a decline in physical activities among them. On the contrary, the greater reduction in fattening food intake among girls accounts for the decrease in their BMI and obesity rate. This study has implications for public health policy. Given that the decrease in physical activity appears to be a major cause of the increase in adolescent BMI and obesity risk after COVID-19, it is essential to provide a safe space for students to exercise. In replacement of outdoor activities with friends, a variety of opportunities should be provided to youth and their families to engage in family physical activities. Second, during remote learning, teachers and school counselors may provide children with practical guidance on how to stay healthy during the pandemic.