Trends in overweight prevalence among university freshmen and the impact of the COVID-19 pandemic: a repeated cross-sectional study.

BACKGROUND

Existing studies on body mass index (BMI) among university students have largely focused on short-term changes during the Coronavirus Disease 2019 (COVID-19) pandemic, with limited evidence on long-term trajectories across different pandemic phases. Therefore, this study aimed to evaluate trends in BMI and overweight prevalence among Chinese university freshmen from 2016 to 2024 using repeated cross-sectional data and to quantify both the immediate and sustained effects of COVID-19 policy transitions.

METHODS

Anthropometric data were collected from successive cohorts of freshmen from a Chinese university between 2016 and 2024. BMI was calculated and categorized into overweight and non-overweight groups. Long-term trends in BMI and overweight prevalence were assessed using linear and non-linear models. Interrupted time series (ITS) analysis was further applied to evaluate changes across the pre-, during-, and post-pandemic periods. Subgroup analyses were conducted by sex and academic discipline.

RESULTS

A total of 39,478 freshmen were included. Overall, a rising trend in BMI and overweight prevalence was observed among university students over the study period. Crude ITS analysis showed that BMI increased gradually before the pandemic (β 1 = 0.096 kg/m2/year, p < 0.001), followed by a temporary slowdown during the pandemic period (β 4 = -0.222 kg/m2/year, p < 0.001). In the post-pandemic period, BMI and overweight prevalence increased markedly, characterized by a significant upward slope change (β 5 = 0.738 kg/m2/year, p = 0.001) reaching the highest levels in 2024. Males exhibited a higher prevalence of overweight and a steeper post-pandemic increase than females. Discipline-specific differences demonstrated that humanities, arts and social sciences (HASS) students had a more immediate change. In contrast, science, technology, engineering, and mathematics (STEM) students exhibited a more sustained increase over time.

CONCLUSION

BMI trajectories were significantly altered by the pandemic, with a marked post-pandemic acceleration exceeding pre-existing trends. Future longitudinal studies are needed to clarify the behavioral mechanisms underlying these trends.