Socioeconomic inequality of obesity in people with type 2 diabetes: the results of DiaCare survey

Obesity is a growing public health concern with significant socioeconomic implications, particularly among people with type 2 diabetes. This study aimed to evaluate socioeconomic inequality in obesity defined by waist circumference (abdominal obesity) and body mass index (BMI) among people with type 2 diabetes, and to examine factors contributing to the observed inequalities, stratified by sex. This cross-sectional study analyzed data from the DiaCare survey of people with type 2 diabetes across Iran using systematic, stratified, and cluster sampling. Validated questionnaires captured socioeconomic status (SES), while anthropometric data assessed obesity. The Erreygers corrected concentration index (ECI) and concentration curves were utilized to represent socioeconomic-related disparities in obesity among individuals with diabetes. Additionally, decomposition analysis was conducted to identify factors contributing to these socioeconomic inequalities in obesity among people with diabetes. A total of 13,321 participants with complete data were included. The prevalence of abdominal obesity (waist circumference-defined) was significantly higher in women (84.2%) than in men (33.2%). Erreygers corrected concentration index showed positive values for both abdominal obesity (women: 0.0331, men: 0.0359) and BMI-defined obesity (women: 0.0786, men: 0.0524), indicating pro-rich socioeconomic inequality. Decomposition analysis revealed that the factors contributing to the observed inequality differed substantially by sex and obesity measure. Among men, belonging to the highest asset quintile was the dominant contributor, accounting for 72.2% of inequality in abdominal obesity and 71.7% in BMI-defined obesity. Among women, urban residence contributed most to inequality (32.2% for abdominal obesity; 38.5% for BMI-defined obesity). Higher education (college or above) was associated with a negative contribution to inequality in men only (− 12.1% for abdominal obesity; −11.3% for BMI-defined obesity), while older age (≥ 65 years) had negative contributions in specific subgroups. Marriage contributed positively to inequality only among men (11.8% for abdominal obesity). In this sample of people with type 2 diabetes in Iran, obesity was disproportionately concentrated among those with higher socioeconomic status, with sex-specific patterns in the factors contributing to the observed inequality. Wealth status accounted for the largest share of the observed inequality among men, whereas urban residence contributed a larger share among women. These findings highlighted sex-specific socioeconomic patterns of obesity among people with diabetes and may help inform future research and the consideration of context-specific approaches to addressing socioeconomic disparities. Given the cross-sectional design and the lack of adjustment for the complex survey design, these findings should be interpreted as associations and contributions to observed inequality rather than causal effects.