China has the largest obese population in the world and its prevalence is increasing faster and faster. The researchers are investigating the association between the socioeconomic status (SES) and obesity in several ways. However, SES may not only play a direct impact on obesity but influences health behaviors which, in turn, affect obesity. The mediating factors have rarely been studied. This study investigates the association between SES and obesity mediated by behavioral factors among adults in China.

The longitudinal data including 110,449 individuals were obtained from the eight waves of the China Health and Nutrition Survey from 1991–2011. The outcome of obesity was measured using Body Mass Index (BMI). The SES factors include education and income (low, medium and high). Mediating factors include alcohol consumption, smoking status, diet and physical activity. A variety of statistical models were used to investigate the association between SES and obesity. Age/gender-adjusted prevalence of obesity was calculated and multiple-logistic regression was used.

To some extent, SES influenced BMI directly, positively in men and inversely in women, respectively. SES may also operate through behavioral factors. These associations were not always straightforward, and changes in SES might create some offsetting risks. Behavioral factors including alcohol consumption, smoking status, diet and physical activity were associated with SES indicators in all groups. In addition, the prevalence was higher in urban areas than rural areas in China. Several pathways for different SES groups leading to obesity were simulated.

Higher SES groups are more likely to have higher BMI compared to lower SES groups. Different SES groups have different significant mediating risk factors. The pathways between SES and obesity are complex. This study suggests that it is necessary to apply different interventions to different SES individuals especially focused on the disadvantaged populations according to their different behaviors and preference.