Obesity and its socioeconomic determinants in Iran

•There is a pro-rich socio-economic inequality in obesity in Iran.•More than 90% of the gap between low and high socioeconomic groups can be attributed to differences in age, gender and marital status.•Results of this study may be useful for policymaking to reduce inequality in obesity. To investigate the socioeconomic inequality of obesity and its determinants in Iran. Data was from Iran's surveillance system for risk factors of non-communicable diseases which was conducted on 89,400 individuals aged 15–64 years in 2005. Principal component analysis was used to create a new variable for defining socioeconomic status of participants. We assessed inequality by calculating a slop index of inequality and concentration index for obesity. Oaxaca-Blinder decomposition analysis was used to determine the determinants of inequality. The slop index of inequality and concentration index for obesity was −13.1 (95% Confidence Intervals [CI]: −16.3 to −9.8) percentage points and −0.123, respectively. The level of inequality varied widely between different provinces in Iran and was more severe in women and urban population. Obesity persisted in 20.2% (95% CI: 19.4–20.9) of the low-socioeconomic group and 11.0% (95% CI: 10.5–11.6) of the high-socioeconomic group. More than 90% of this gap was due to differences of independent variables (mainly age, gender and marital status) in two socioeconomic status groups. A pro-rich inequality existed in the obesity in Iran. Older age, female gender and rural residency contributed most to the economic inequality of obesity.