Participants characteristics from CGSS.

Background
Adults living alone represent a growing population group in China. Understanding the prevalence of body mass index (BMI) categories and their associations with demographic and lifestyle factors among this group is essential for informing targeted interventions and public health policies.
Methods
In this population-based cross-sectional study, we used individual-level data from the 2011–2021 China General Social Survey. Main outcomes were prevalence of BMI categories adjusted for gender and age, using logistic regression and model-predicted marginal prevalence to estimate BMI categories prevalence.
Results
We analyzed 9,077 single-living Chinese adult participants. The primary-adjusted prevalence of BMI categories varied across different genders and age groups. Underweight was more prevalent in females (12.73%; 95% CI: 12.31% - 13.14%) than in males (7.54%; 95% CI: 7.19% - 7.88%), while overweight and obesity were higher in males. Primary-adjusted underweight prevalence was highest among the 18–24 years age group (22.09%; 95% CI: 20.17% - 24.01%) and decreased with age. Primary-adjusted overweight prevalence increased with age, peaking in the 45–54 years age group (41.94%; 95% CI: 40.96% - 42.93%). Primary-adjusted obesity prevalence exhibited a fluctuating pattern across age groups, with the highest prevalence observed in the 45–54 years age group (9.81%; 95% CI: 9.19% - 10.44%).
Conclusion
Our findings reveal significant associations between BMI categories and demographic and lifestyle factors among adults living alone in China. These results can inform targeted interventions and public health policies aimed at promoting healthy weight management and addressing the unique health challenges faced by single-living individuals in China.