Patterns of change in the association between socioeconomic status and body mass index distribution in India, 1999-2021.

Background: Body mass index (BMI) is an important indicator of human health. However, trends in socioeconomic inequalities in BMI over time throughout India are understudied. Filling this gap will elucidate which socioeconomic groups are still at risk for adverse BMI values. Methods: This repeated cross-sectional study analysed four rounds of India's National Family Health Surveys (1998-1999, 2005-2006, 2015-2016, and 2019-2021). The outcome was BMI categories, measured in kilogram per metres squared (kg/m Results: The study population consisted of 1 244 149 women and 227 585 men. We found that those in the lowest SES categories were more likely to be severely/moderately thin or mildly thin. Conversely, those in the highest SES groups were more likely to be overweight or obese. The gradients were steepest for wealth, and this was substantiated by the results of regression models for every wave. There has been a decline in the difference in the prevalence of severely/moderately thin or mildly thin between SES groups when comparing the years 1999 and 2021. Conclusions: SES-based inequalities in BMI were smaller in 2021 compared to 1999. However, those in low SES groups were most likely to be severely/moderately thin or mildly thin while those in high SES groups were more likely to be overweight or obese. Future research should explore the pathways that link SES with BMI.